Speed up native AST materialization (#388)

## Summary
- reuse one `WP_MySQL_Parser` instance inside the SQLite driver and
reset its token stream per query
- add `reset_tokens()` to the PHP parser polyfill and the Rust native
parser
- restore native parser-node accessor fast paths in
`WP_MySQL_Native_Parser_Node`, while keeping PHP child materialization
for mutation
- fix the local native extension build helper for Nix/libclang bindgen
by undefining `__SSE2__` during binding generation

## Stack
This is the top PR in the native MySQL lexer/parser stack. The stack is
split so each GitHub diff shows one reviewable concern:

1. [#384 Extract MySQL lexer and parser
polyfills](#384)
   - `trunk` -> `codex/native-parser-php-facade`
   - extraction-only PHP refactor
- moves the existing PHP lexer/parser implementations into polyfill
classes
- keeps public `WP_MySQL_Lexer` and `WP_MySQL_Parser` as thin PHP
subclasses

2. [#385 Add optional native parser
routing](#385)
- `codex/native-parser-php-facade` ->
`codex/native-parser-class-routing`
   - adds fallback `WP_MySQL_Native_*` PHP classes
- routes the public lexer/parser classes through native classes when the
Rust extension provides them
   - adds the minimal PHP grammar-export bridge for the native parser

3. [#386 Add lazy native parser node
facade](#386)
- `codex/native-parser-class-routing` ->
`codex/native-parser-node-facade`
   - keeps `WP_Parser_Node` as the plain PHP tree node
- adds `WP_MySQL_Native_Parser_Node extends WP_Parser_Node` for
native-backed lazy AST nodes
- keeps native AST handles and native accessor delegation out of the
base node class

4. [#381 Add lazy native AST
facade](#381)
   - `codex/native-parser-node-facade` -> `codex/native-lazy-ast-facade`
- implements the Rust lexer/parser extension and lazy native AST facade
   - makes the Rust extension instantiate `WP_MySQL_Native_Parser_Node`
- adds native-extension CI coverage for the SQLite driver and WordPress
PHPUnit tests
   - includes the local SQLite facade smoke benchmark

5. [#387 Cache native grammar on parser grammar
object](#387)
- `codex/native-lazy-ast-facade` ->
`codex/native-parser-object-grammar-cache`
   - restores the object-attached native grammar cache
   - adds only `WP_Parser_Grammar::$native_grammar` on the PHP side
- removes the Rust content-hash cache that walked the whole exported
grammar on every parser construction

6. This PR, [#388 Speed up native AST
materialization](#388)
- `codex/native-parser-object-grammar-cache` ->
`codex/native-parser-bulk-materialization`
- optimizes native-to-PHP AST access after the grammar-cache performance
restoration
- reuses the SQLite driver's parser instance instead of constructing it
per query

## Why
The native lexer/parser itself is fast, but the PHP-facing path can lose
that benefit if each query repeatedly rebuilds native parser state or
forces full PHP AST materialization. On the current stack, #387 already
removes the large grammar export/hash cost. This PR removes the
remaining per-query parser construction churn and restores the native
AST accessor path for descendant-heavy SQLite driver workloads.

## Measurements
Environment: local PHP 8.2 via the native build helper, release Rust
extension, current top of this PR.

Focused constructor/reset benchmark over 5000 unique SELECT queries:

| Phase | Time |
| --- | ---: |
| native tokenize | 22.62 us/query |
| fresh native parser constructor only | 2.31 us/query |
| reusable parser `reset_tokens()` only | 0.32 us/query |
| reusable parser reset + parse + `get_descendants()` | 157.06 us/query
|
| constructor/reset ratio | 7.3x |

The previously reported ~622 us/query constructor cost does not
reproduce on this stack because #387 already caches the native grammar
on the PHP grammar object. Parser reuse still removes most of the
remaining constructor overhead.

SQLite facade smoke workload:

Command:

```bash
TMP_TEST_NATIVE_QUERY_COUNT=250 ./tmp-test-native/run.sh
```

| Workload | PHP fallback | Native extension | Speedup |
| --- | ---: | ---: | ---: |
| 250 generated queries, including 1 x 2000-row insert | 4.060s | 0.525s
| 7.73x |

## Testing
- `cargo fmt --check`
- `git diff --check`
- `composer run check-cs`
- `composer run test` from `packages/mysql-on-sqlite`
- `php -d
extension=packages/mysql-on-sqlite/ext/wp-mysql-parser/target/release/libwp_mysql_parser.so
packages/mysql-on-sqlite/vendor/bin/phpunit -c
packages/mysql-on-sqlite/phpunit.xml.dist`
- `TMP_TEST_NATIVE_QUERY_COUNT=250 ./tmp-test-native/run.sh`

Author: adamziel

.github/workflows/mysql-parser-extension-tests.yml

@@ -81,7 +81,10 @@ jobs:
               exit( 1 );
           }
           '
-          ./vendor/bin/phpunit -c ./phpunit.xml.dist tests/mysql/WP_MySQL_Lexer_Tests.php tests/parser/WP_Parser_Node_Tests.php
+        working-directory: packages/mysql-on-sqlite
+
+      - name: Run PHPUnit tests with parser extension
+        run: php -d extension="$GITHUB_WORKSPACE/packages/php-ext-wp-mysql-parser/target/debug/libwp_mysql_parser.so" ./vendor/bin/phpunit -c ./phpunit.xml.dist
         working-directory: packages/mysql-on-sqlite
 
   sqlite-driver-extension-tests:
@@ -149,3 +152,7 @@ jobs:
               exit( 1 );
           }
           '
+
+      - name: Run PHPUnit tests with SQLite driver using parser extension
+        run: php -d extension="$GITHUB_WORKSPACE/packages/php-ext-wp-mysql-parser/target/debug/libwp_mysql_parser.so" ./vendor/bin/phpunit -c ./phpunit.xml.dist
+        working-directory: packages/mysql-on-sqlite

.github/workflows/wp-tests-phpunit.yml

@@ -54,8 +54,8 @@ jobs:
       - name: Build and load parser extension in WordPress PHP containers
         run: bash .github/workflows/wp-tests-phpunit-native-extension-setup.sh
 
-      - name: Verify WordPress uses parser extension
-        run: cd wordpress && node tools/local-env/scripts/docker.js run --rm php php /var/www/native-verify-extension.php
+      - name: Run WordPress PHPUnit tests with parser extension
+        run: node .github/workflows/wp-tests-phpunit-run.js
 
       - name: Stop Docker containers
         if: always()

packages/mysql-on-sqlite/src/mysql/class-wp-mysql-parser.php

@@ -8,6 +8,17 @@ class WP_MySQL_Parser extends WP_Parser {
 	 */
 	private $current_ast;
 
+	/**
+	 * Reset this parser with a new token stream.
+	 *
+	 * @param array<WP_Parser_Token> $tokens The parser tokens.
+	 */
+	public function reset_tokens( array $tokens ): void {
+		$this->tokens      = $tokens;
+		$this->position    = 0;
+		$this->current_ast = null;
+	}
+
 	/**
 	 * Parse the next query from the input SQL string.
 	 *

packages/mysql-on-sqlite/src/sqlite/class-wp-pdo-mysql-on-sqlite.php

@@ -410,6 +410,13 @@ class WP_PDO_MySQL_On_SQLite extends PDO {
 	 */
 	private static $mysql_grammar;
 
+	/**
+	 * A reusable parser instance for MySQL queries.
+	 *
+	 * @var WP_MySQL_Parser|null
+	 */
+	private $mysql_parser = null;
+
 	/**
 	 * The main database name.
 	 *
@@ -1160,11 +1167,27 @@ public function create_parser( string $query ): WP_MySQL_Parser {
 		);
 		if ( $lexer instanceof WP_MySQL_Native_Lexer ) {
 			$tokens = $lexer->native_token_stream();
-			return new WP_MySQL_Parser( self::$mysql_grammar, $tokens );
+			return $this->reset_or_create_parser( $tokens );
 		}
 
 		$tokens = $lexer->remaining_tokens();
-		return new WP_MySQL_Parser( self::$mysql_grammar, $tokens );
+		return $this->reset_or_create_parser( $tokens );
+	}
+
+	/**
+	 * Reset the reusable parser with new tokens or create it on first use.
+	 *
+	 * @param  array<WP_Parser_Token>|object $tokens Parser tokens.
+	 * @return WP_MySQL_Parser                       A parser initialized for the token stream.
+	 */
+	private function reset_or_create_parser( $tokens ): WP_MySQL_Parser {
+		if ( null === $this->mysql_parser || ! method_exists( $this->mysql_parser, 'reset_tokens' ) ) {
+			$this->mysql_parser = new WP_MySQL_Parser( self::$mysql_grammar, $tokens );
+		} else {
+			$this->mysql_parser->reset_tokens( $tokens );
+		}
+
+		return $this->mysql_parser;
 	}
 
 	/**