feat(pdftract-2bs4j): implement PDF/A conformance detection via XMP parsing
- Add detect_conformance() to parse pdfaid:part and pdfaid:conformance from XMP /Metadata stream
- Support all PDF/A levels: 1a/b, 2a/b/u/f, 3a/b/u/f, 4e/f
- Namespace-agnostic matching handles any prefix (pdfaid, x, foo, etc.)
- Graceful failure: malformed XML returns None (INV-8 compliant)
- quick-xml already in default dependencies (line 46 of Cargo.toml)
- 15 comprehensive tests covering all acceptance criteria
Acceptance criteria status:
- PDF/A-1b, 2u, 3a, 4e, 4f detection: PASS
- Part-only detection: PASS
- No metadata/malformed XML: PASS
- Different namespace prefixes: PASS
Verification note: notes/pdftract-2bs4j.md
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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