feat(kernel): R7b Rust walker — rustlang module, tree-sitter-rust 0.24.2 bump, rust default-routed (#1371)

First R7b language port. Grammar: tree-sitter-rust pinned =0.24.2 + wasm
vendored from tag 77a3747 (parser.c/scanner.c sha-matched against the
crates.io tarball), replacing the 2023 ABI-14 tree-sitter-wasms build —
the bump alone is precision-positive on the wasm path (receiver-qualified
instance-method resolutions replace ambiguous bare-name matches; node
sections byte-identical on ripgrep/tokio).

Walker mirrors the TS reference bug-for-bug per
docs/design/rust-lang-kernel-port-checklist.md (survey artifact): dead-code
isAsync, impl-pushes-no-scope, the impl-Trait-for-Generic<T> trait-receiver
quirk, phantom const identifiers, use-binding triple emission,
wildcard-use-emits-nothing, scoped-supertrait drop, chained-call re-encode
gated on scoped_identifier, Rocket route macros body-only.

Gates: parity sweeps 0 diffs — ripgrep 101/101, tokio 790/790,
rust-analyzer 1217/1488 (271 deferrals are token-macro-table sources that
error on BOTH arms — grammar-inherent); full-init dump-diffs byte-identical
on all three (3,857 / 13,440 / 39,030 nodes); kernel-rustlang-parity suite
(torture + CRLF + defer) in npm test; full suite green x2 with
CODEGRAPH_KERNEL_EXPECT=1.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

__tests__/kernel-grammar-parity.test.ts

@@ -36,7 +36,7 @@ const kernelBuilt = fs.existsSync(KERNEL_PATH);
 
 // Every kernel-capable language. `jsx` shares the javascript grammar on BOTH
 // paths (langs.rs mirrors WASM_GRAMMAR_FILES), so the distinct grammars are:
-const GRAMMAR_LANGUAGES: Language[] = ['typescript', 'tsx', 'javascript', 'java', 'python', 'go', 'c', 'cpp'];
+const GRAMMAR_LANGUAGES: Language[] = ['typescript', 'tsx', 'javascript', 'java', 'python', 'go', 'c', 'cpp', 'rust'];
 
 describe.skipIf(!kernelBuilt)('kernel↔wasm grammar parity', () => {
   beforeAll(async () => {