perf(source): record parents during traversal instead of re-walking from the root

tree-sitter's `Node::parent` re-descends from the root, so each call is
O(depth), and `enclosing_function`, `lexical_scope` and
`parameter_shadows` walked ancestors through it for every call site and
declaration: extraction time grew quadratically with nesting depth
(sample profile: >90% of time in ts_node_parent under those three).

The main traversal now records each node's parent, and the three
ancestor walks look it up (falling back to `Node::parent` for nodes the
traversal skips, so results are unchanged).

Measured on one C++ file with a call nested N blocks deep (release,
macOS arm64): N=2.5k/5k/10k/20k took 0.26/1.05/4.24/16.8 s before;
after, 20k takes 0.02 s with the same nodes and call edge. The full
suite (111 tests) passes unchanged.

src/source.rs

@@ -242,6 +242,9 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
     // Iterative traversal avoids a Rust stack overflow on deeply nested source.
     // Error subtrees are omitted; complete sibling declarations remain usable.
     let mut nodes = Vec::new();
+    // Parent of every traversed node. tree-sitter's `Node::parent` re-descends from
+    // the root (O(depth)), so ancestor walks through it were quadratic in nesting.
+    let mut parents: HashMap<usize, Node<'_>> = HashMap::new();
     let mut errors: Vec<(usize, usize)> = Vec::new();
     let mut stack = vec![tree.root_node()];
     while let Some(node) = stack.pop() {
@@ -312,6 +315,9 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
         }
         let mut cursor = node.walk();
         let children: Vec<_> = node.named_children(&mut cursor).collect();
+        for child in &children {
+            parents.insert(child.id(), node);
+        }
         stack.extend(children.into_iter().rev());
     }
     // Anonymous MISSING tokens (`#endif`, `;`, `}`) are not named children; find
@@ -395,7 +401,7 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
                 name,
                 kind,
                 owner: None,
-                scope: lexical_scope(node, source),
+                scope: lexical_scope(node, source, &parents),
                 line: node.start_position().row + 1,
                 identity,
                 qualifier,
@@ -418,7 +424,7 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
                 let ty = ancestor
                     .child_by_field_name("type")
                     .map(|n| base_type(n, source));
-                let scope = lexical_scope(ancestor, source);
+                let scope = lexical_scope(ancestor, source, &parents);
                 let candidates: Vec<_> = doc
                     .declarations
                     .iter()
@@ -431,7 +437,13 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
                                 declaration_nodes[*i],
                                 &declarations,
                                 &doc.declarations,
-                            ) == enclosing_function(ancestor, &declarations, &doc.declarations)
+                                &parents,
+                            ) == enclosing_function(
+                                ancestor,
+                                &declarations,
+                                &doc.declarations,
+                                &parents,
+                            )
                     })
                     .map(|(i, _)| i)
                     .collect();
@@ -474,8 +486,8 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
         {
             continue;
         }
-        let owner = enclosing_function(node, &declarations, &doc.declarations);
+        let owner = enclosing_function(node, &declarations, &doc.declarations, &parents);
-        let scope = lexical_scope(node, source);
+        let scope = lexical_scope(node, source, &parents);
         if language == "rust" && node.kind() == "use_declaration" && !has_error(node) {
             for (target, binding) in rust_imports(node, source) {
                 if owner.is_none() {
@@ -539,7 +551,7 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
             for (target, line) in cpp_vexing_calls(node, source) {
                 doc.relationships.push(Relationship {
                     owner,
-                    shadowed: parameter_shadows(node, &target, source),
+                    shadowed: parameter_shadows(node, &target, source, &parents),
                     target,
                     kind: EdgeKind::Calls,
                     member: false,
@@ -580,6 +592,7 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
             if node.kind() == "macro_invocation" {
                 let context = MacroContext {
                     position: node,
+                    parents: &parents,
                     owner,
                     scope: &scope,
                     self_type: &self_type,
@@ -632,7 +645,7 @@ pub(crate) fn extract(language: &str, path: &str, source: &str) -> Result<Docume
                     None
                 };
                 doc.relationships.push(Relationship {
-                    shadowed: !member && parameter_shadows(node, &target, source),
+                    shadowed: !member && parameter_shadows(node, &target, source, &parents),
                     owner,
                     target,
                     member,
@@ -832,8 +845,20 @@ fn cpp_leaf_name(name: Node<'_>, source: &str) -> Option<String> {
     Some(text(name, source).to_owned())
 }
 
-fn lexical_scope(node: Node<'_>, source: &str) -> String {
+/// The parent recorded during traversal, else tree-sitter's (O(depth)) lookup.
-    let mut parent = node.parent();
+fn parent_of<'tree>(
+    node: Node<'tree>,
+    parents: &HashMap<usize, Node<'tree>>,
+) -> Option<Node<'tree>> {
+    parents.get(&node.id()).copied().or_else(|| node.parent())
+}
+
+fn lexical_scope<'tree>(
+    node: Node<'tree>,
+    source: &str,
+    parents: &HashMap<usize, Node<'tree>>,
+) -> String {
+    let mut parent = parent_of(node, parents);
     let mut names = Vec::new();
     while let Some(n) = parent {
         if matches!(
@@ -846,25 +871,26 @@ fn lexical_scope(node: Node<'_>, source: &str) -> String {
                     .unwrap_or("<anonymous>"),
             );
         }
-        parent = n.parent();
+        parent = parent_of(n, parents);
     }
     names.reverse();
     names.join("::")
 }
 
-fn enclosing_function(
+fn enclosing_function<'tree>(
-    node: Node<'_>,
+    node: Node<'tree>,
     ids: &HashMap<usize, usize>,
     declarations: &[Declaration],
+    parents: &HashMap<usize, Node<'tree>>,
 ) -> Option<usize> {
-    let mut parent = node.parent();
+    let mut parent = parent_of(node, parents);
     while let Some(n) = parent {
         if let Some(&index) = ids.get(&n.id())
             && declarations[index].kind == NodeKind::Function
         {
             return Some(index);
         }
-        parent = n.parent();
+        parent = parent_of(n, parents);
     }
     None
 }
@@ -1023,8 +1049,13 @@ fn exported_names(node: Node<'_>, name: &str) -> Vec<String> {
     Vec::new()
 }
 
-fn parameter_shadows(node: Node<'_>, name: &str, source: &str) -> bool {
+fn parameter_shadows<'tree>(
-    let mut parent = node.parent();
+    node: Node<'tree>,
+    name: &str,
+    source: &str,
+    parents: &HashMap<usize, Node<'tree>>,
+) -> bool {
+    let mut parent = parent_of(node, parents);
     while let Some(n) = parent {
         let signature = n
             .child_by_field_name("signature")
@@ -1058,7 +1089,7 @@ fn parameter_shadows(node: Node<'_>, name: &str, source: &str) -> bool {
                 );
             }
         }
-        parent = n.parent();
+        parent = parent_of(n, parents);
     }
     false
 }
@@ -1090,7 +1121,7 @@ fn import_bindings(node: Node<'_>, module: &str, source: &str) -> Vec<ImportBind
                 local: local.into(),
                 exported: exported.into(),
                 module: module.into(),
-                scope: lexical_scope(node, source),
+                scope: lexical_scope(node, source, &HashMap::new()),
             });
         }
         let mut cursor = n.walk();
@@ -1160,7 +1191,7 @@ fn rust_imports(node: Node<'_>, source: &str) -> Vec<(String, Option<ImportBindi
                         local,
                         exported: exported.into(),
                         module: module.into(),
-                        scope: lexical_scope(node, source),
+                        scope: lexical_scope(node, source, &HashMap::new()),
                     })
                 };
                 output.push((target, binding));
@@ -1847,6 +1878,7 @@ fn rust_fields(node: Node<'_>, source: &str) -> Vec<(String, String, CppType)> {
 
 struct MacroContext<'a, 'tree> {
     position: Node<'tree>,
+    parents: &'a HashMap<usize, Node<'tree>>,
     owner: Option<usize>,
     scope: &'a str,
     self_type: &'a Option<String>,
@@ -1943,7 +1975,12 @@ fn rust_macro_calls(
                 });
                 relationships.push(Relationship {
                     shadowed: !member
-                        && parameter_shadows(context.position, &target, context.source),
+                        && parameter_shadows(
+                            context.position,
+                            &target,
+                            context.source,
+                            context.parents,
+                        ),
                     owner: context.owner,
                     target,
                     member,