Set up test infrastructure with html5lib and Test262 harnesses
Add html5lib-tests and Test262 as git submodules under tests/.
Create integration test harnesses for both suites:
- html5lib tokenizer harness (we-html): reads JSON test files,
runs each case against our tokenizer stub, reports pass/fail/skip.
Includes a minimal JSON parser (no external crates).
- Test262 harness (we-js): walks JS test files, parses YAML
frontmatter for metadata, runs each case against our evaluate()
stub, reports pass/fail/skip grouped by category.
Both harnesses work with empty implementations (0% pass rate on
positive tests) and will track progress as features are implemented.
Adds Token enum and tokenize() stub to we-html.
Adds JsError and evaluate() stub to we-js.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>