Add comprehensive test coverage for JavaScript, XFA, and conformance detection:
- JS detection tests: annotation /A, page /AA, AcroForm field /AA
- XFA detection tests: null, array, present, absent cases
- Conformance detection tests: PDF/A-1b/2u/3a/4e/4f, malformed XML, no metadata
Enhance conformance detection with diagnostic emission for malformed XMP:
- Emit STRUCT_INVALID_XMP when XMP XML is malformed
- Graceful failure returns None without panic (INV-8)
quick-xml already in default features (verified via cargo tree)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
fba1b07caf