Compare exact case-sensitive attribute values directly

[jdalton]

Tooling update

Rebased onto merged #212 as one commit. Sources and tests use .mts, Node tests use Vitest, and the published JavaScript paths stay unchanged. The original engine changes are preserved.

Local lint, formatting, Node and packed-package checks pass. All 41 WPT pages pass against both generated builds.

Change

Compare exact, case-sensitive attribute values as strings instead of running a regular expression for each candidate. Case-insensitive matches and other operators keep their existing path.

Extracted from #167 without its legacy helpers or tag-ordering changes. The attribute name stays separate from the decoded value, fixing the aggregate's case-rule regression. Quoted values retain JavaScript escapes without double-escaping quotes.

Validation covers HTML case-insensitive attributes, custom data attributes, explicit i, empty and missing attributes, escaped values, XML, SVG, cached queries, and a custom operator. Compilation checks confirm the direct comparison is emitted. All three tests pass with Chromium enabled, including ten native-browser comparisons.

Run with Node.js ≥ 22. Commands are in test/attribute-equality.md. No end-to-end speedup is claimed without a benchmark.

[jdalton]

Integrated the current legacy helpers and added WPT coverage for exact values, escapes, HTML/XML case rules, SVG, and custom operators. A new cross-document test exposed cached HTML case rules being reused for XML; the PR now invalidates document-specific plans when the document changes. All 470 Node tests and 52 WPT pages pass, and CI is green. Coverage thresholds are unchanged.