Add tests for PHP runnable queries

[roxblnfk]

What

Adds a cargo test suite that exercises languages/php/runnables.scm and languages/php/tasks.json, so the runnable/gutter queries have coverage and regressions get caught before release. There are no tests for the runnable queries today, so it's easy to break gutter detection (or the tag ↔ task wiring) without noticing until it ships.

How

Mirrors the approach already used by zed-extensions/java: runs the shipped .scm with the native tree-sitter engine over the pinned grammar, as dev-dependencies. The grammar commit in extension.toml (5b5627f) is the tree-sitter-php 0.24.2 release, so the crate parses identically to the editor.

One deliberate detail: the helper calls cursor.set_match_limit(64) to mirror QueryCursorHandle::new() in crates/language/src/syntax_map.rs, so tests see the same match-limit behaviour Zed applies at runtime.

• tests/support/mod.rs — run_query helper (parse → query → collect @run captures with their tag and row).
• tests/runnables.rs — PHPUnit (naming convention, @test, #[Test], abstract) and Pest.
• tests/tasks.rs — every (#set! tag …) in the query has a matching task in tasks.json, and tags map to the expected runner.

No workflow is added: the org-wide extension_tests workflow already runs cargo nextest on pull requests, so these tests are picked up automatically.

Documented gaps (#[ignore]d)

Two #[ignore]d tests pin behaviour the current query gets wrong — it tags things as PHPUnit that most likely aren't:

• a *Test class with no extends (PHPUnit test cases always inherit from TestCase; a class with no base class is far more likely a non-PHPUnit test);
• a bare #[Test] method in such a class (#[Test] is ambiguous between PHPUnit\Framework\Attributes\Test and other frameworks).

They assert the intended behaviour, so they fail today and are skipped in CI. Run them with cargo test -- --ignored to see the gaps.

While writing these I also noticed the (#not-any-eq? @_modifier "abstract") guard on the PHPUnit patterns never fires with the pinned grammar — abstract *Test classes are still tagged. That's pinned as-is by abstract_test_class_is_tagged (the gutter is harmless — PHPUnit just won't run an abstract class), but worth flagging.

Running

cargo test                 # 8 pass, 2 ignored
cargo test -- --ignored    # runs the two documented-gap tests (they fail today)