Created forms/xfa.rs module with extract_xfa_fields() that:
- Handles single-stream and array-stream XFA layouts
- Uses quick-xml for XML parsing with namespace support
- Extracts field values from XFA data model (xfa:datasets/xfa:data)
- Supports FlateDecode-compressed streams via Phase 1 decoder
- Returns Vec<XfaField> with dot-separated field names
Acceptance criteria:
- Critical test: XFA-only form field values extracted
- Unit tests: single stream, array stream, malformed XML, empty fields
- Public API: extract_xfa_fields(resolver, acroform_dict, source, opts)
- quick-xml feature flags: enabled via existing 'ocr' feature
All tests pass. Closes: pdftract-28e9
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
