[ty] AST garbage collection (#18482)

## Summary

Garbage collect ASTs once we are done checking a given file. Queries
with a cross-file dependency on the AST will reparse the file on demand.
This reduces ty's peak memory usage by ~20-30%.

The primary change of this PR is adding a `node_index` field to every
AST node, that is assigned by the parser. `ParsedModule` can use this to
create a flat index of AST nodes any time the file is parsed (or
reparsed). This allows `AstNodeRef` to simply index into the current
instance of the `ParsedModule`, instead of storing a pointer directly.

The indices are somewhat hackily (using an atomic integer) assigned by
the `parsed_module` query instead of by the parser directly. Assigning
the indices in source-order in the (recursive) parser turns out to be
difficult, and collecting the nodes during semantic indexing is
impossible as `SemanticIndex` does not hold onto a specific
`ParsedModuleRef`, which the pointers in the flat AST are tied to. This
means that we have to do an extra AST traversal to assign and collect
the nodes into a flat index, but the small performance impact (~3% on
cold runs) seems worth it for the memory savings.

Part of https://github.com/astral-sh/ty/issues/214.

crates/ruff_python_formatter/src/statement/clause.rs

@@ -87,6 +87,7 @@ impl ClauseHeader<'_> {
                 type_params,
                 arguments,
                 range: _,
+                node_index: _,
                 decorator_list: _,
                 name: _,
                 body: _,
@@ -103,6 +104,7 @@ impl ClauseHeader<'_> {
                 type_params,
                 parameters,
                 range: _,
+                node_index: _,
                 is_async: _,
                 decorator_list: _,
                 name: _,
@@ -121,6 +123,7 @@ impl ClauseHeader<'_> {
             ClauseHeader::If(StmtIf {
                 test,
                 range: _,
+                node_index: _,
                 body: _,
                 elif_else_clauses: _,
             }) => {
@@ -129,6 +132,7 @@ impl ClauseHeader<'_> {
             ClauseHeader::ElifElse(ElifElseClause {
                 test,
                 range: _,
+                node_index: _,
                 body: _,
             }) => {
                 if let Some(test) = test.as_ref() {
@@ -139,6 +143,7 @@ impl ClauseHeader<'_> {
             ClauseHeader::ExceptHandler(ExceptHandlerExceptHandler {
                 type_: type_expr,
                 range: _,
+                node_index: _,
                 name: _,
                 body: _,
             }) => {
@@ -149,6 +154,7 @@ impl ClauseHeader<'_> {
             ClauseHeader::Match(StmtMatch {
                 subject,
                 range: _,
+                node_index: _,
                 cases: _,
             }) => {
                 visit(subject.as_ref(), visitor);
@@ -157,6 +163,7 @@ impl ClauseHeader<'_> {
                 guard,
                 pattern,
                 range: _,
+                node_index: _,
                 body: _,
             }) => {
                 visit(pattern, visitor);
@@ -169,6 +176,7 @@ impl ClauseHeader<'_> {
                 target,
                 iter,
                 range: _,
+                node_index: _,
                 is_async: _,
                 body: _,
                 orelse: _,
@@ -179,6 +187,7 @@ impl ClauseHeader<'_> {
             ClauseHeader::While(StmtWhile {
                 test,
                 range: _,
+                node_index: _,
                 body: _,
                 orelse: _,
             }) => {
@@ -187,6 +196,7 @@ impl ClauseHeader<'_> {
             ClauseHeader::With(StmtWith {
                 items,
                 range: _,
+                node_index: _,
                 is_async: _,
                 body: _,
             }) => {

crates/ruff_python_formatter/src/statement/stmt_ann_assign.rs

@@ -17,6 +17,7 @@ impl FormatNodeRule<StmtAnnAssign> for FormatStmtAnnAssign {
     fn fmt_fields(&self, item: &StmtAnnAssign, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtAnnAssign {
             range: _,
+            node_index: _,
             target,
             annotation,
             value,

crates/ruff_python_formatter/src/statement/stmt_assert.rs

@@ -14,6 +14,7 @@ impl FormatNodeRule<StmtAssert> for FormatStmtAssert {
     fn fmt_fields(&self, item: &StmtAssert, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtAssert {
             range: _,
+            node_index: _,
             test,
             msg,
         } = item;

crates/ruff_python_formatter/src/statement/stmt_assign.rs

@@ -33,6 +33,7 @@ impl FormatNodeRule<StmtAssign> for FormatStmtAssign {
     fn fmt_fields(&self, item: &StmtAssign, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtAssign {
             range: _,
+            node_index: _,
             targets,
             value,
         } = item;

crates/ruff_python_formatter/src/statement/stmt_aug_assign.rs

@@ -21,6 +21,7 @@ impl FormatNodeRule<StmtAugAssign> for FormatStmtAugAssign {
             op,
             value,
             range: _,
+            node_index: _,
         } = item;
 
         if has_target_own_parentheses(target, f.context())

crates/ruff_python_formatter/src/statement/stmt_class_def.rs

@@ -18,6 +18,7 @@ impl FormatNodeRule<StmtClassDef> for FormatStmtClassDef {
     fn fmt_fields(&self, item: &StmtClassDef, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtClassDef {
             range: _,
+            node_index: _,
             name,
             arguments,
             body,

crates/ruff_python_formatter/src/statement/stmt_delete.rs

@@ -13,7 +13,11 @@ pub struct FormatStmtDelete;
 
 impl FormatNodeRule<StmtDelete> for FormatStmtDelete {
     fn fmt_fields(&self, item: &StmtDelete, f: &mut PyFormatter) -> FormatResult<()> {
-        let StmtDelete { range: _, targets } = item;
+        let StmtDelete {
+            range: _,
+            node_index: _,
+            targets,
+        } = item;
 
         write!(f, [token("del"), space()])?;
 

crates/ruff_python_formatter/src/statement/stmt_for.rs

@@ -36,6 +36,7 @@ impl FormatNodeRule<StmtFor> for FormatStmtFor {
             body,
             orelse,
             range: _,
+            node_index: _,
         } = item;
 
         let comments = f.context().comments().clone();

crates/ruff_python_formatter/src/statement/stmt_function_def.rs

@@ -93,6 +93,7 @@ impl FormatNodeRule<StmtFunctionDef> for FormatStmtFunctionDef {
 fn format_function_header(f: &mut PyFormatter, item: &StmtFunctionDef) -> FormatResult<()> {
     let StmtFunctionDef {
         range: _,
+        node_index: _,
         is_async,
         decorator_list: _,
         name,

crates/ruff_python_formatter/src/statement/stmt_if.rs

@@ -15,6 +15,7 @@ impl FormatNodeRule<StmtIf> for FormatStmtIf {
     fn fmt_fields(&self, item: &StmtIf, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtIf {
             range: _,
+            node_index: _,
             test,
             body,
             elif_else_clauses,
@@ -68,6 +69,7 @@ pub(crate) fn format_elif_else_clause(
 ) -> FormatResult<()> {
     let ElifElseClause {
         range: _,
+        node_index: _,
         test,
         body,
     } = item;

crates/ruff_python_formatter/src/statement/stmt_import.rs

@@ -9,7 +9,11 @@ pub struct FormatStmtImport;
 
 impl FormatNodeRule<StmtImport> for FormatStmtImport {
     fn fmt_fields(&self, item: &StmtImport, f: &mut PyFormatter) -> FormatResult<()> {
-        let StmtImport { names, range: _ } = item;
+        let StmtImport {
+            names,
+            range: _,
+            node_index: _,
+        } = item;
         let names = format_with(|f| {
             f.join_with(&format_args![token(","), space()])
                 .entries(names.iter().formatted())

crates/ruff_python_formatter/src/statement/stmt_import_from.rs

@@ -19,6 +19,7 @@ impl FormatNodeRule<StmtImportFrom> for FormatStmtImportFrom {
             names,
             level,
             range: _,
+            node_index: _,
         } = item;
 
         write!(

crates/ruff_python_formatter/src/statement/stmt_match.rs

@@ -15,6 +15,7 @@ impl FormatNodeRule<StmtMatch> for FormatStmtMatch {
     fn fmt_fields(&self, item: &StmtMatch, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtMatch {
             range: _,
+            node_index: _,
             subject,
             cases,
         } = item;

crates/ruff_python_formatter/src/statement/stmt_raise.rs

@@ -13,6 +13,7 @@ impl FormatNodeRule<StmtRaise> for FormatStmtRaise {
     fn fmt_fields(&self, item: &StmtRaise, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtRaise {
             range: _,
+            node_index: _,
             exc,
             cause,
         } = item;

crates/ruff_python_formatter/src/statement/stmt_return.rs

@@ -11,7 +11,11 @@ pub struct FormatStmtReturn;
 
 impl FormatNodeRule<StmtReturn> for FormatStmtReturn {
     fn fmt_fields(&self, item: &StmtReturn, f: &mut PyFormatter) -> FormatResult<()> {
-        let StmtReturn { range: _, value } = item;
+        let StmtReturn {
+            range: _,
+            node_index: _,
+            value,
+        } = item;
 
         token("return").fmt(f)?;
 

crates/ruff_python_formatter/src/statement/stmt_try.rs

@@ -66,6 +66,7 @@ impl FormatNodeRule<StmtTry> for FormatStmtTry {
             finalbody,
             is_star,
             range: _,
+            node_index: _,
         } = item;
 
         let comments_info = f.context().comments().clone();

crates/ruff_python_formatter/src/statement/stmt_type_alias.rs

@@ -17,6 +17,7 @@ impl FormatNodeRule<StmtTypeAlias> for FormatStmtTypeAlias {
             type_params,
             value,
             range: _,
+            node_index: _,
         } = item;
 
         write!(f, [token("type"), space(), name.as_ref().format()])?;

crates/ruff_python_formatter/src/statement/stmt_while.rs

@@ -15,6 +15,7 @@ impl FormatNodeRule<StmtWhile> for FormatStmtWhile {
     fn fmt_fields(&self, item: &StmtWhile, f: &mut PyFormatter) -> FormatResult<()> {
         let StmtWhile {
             range: _,
+            node_index: _,
             test,
             body,
             orelse,