Add call-site diagnostic emission for DCTDecode SOI/EOI marker validation.
Previously, DCTDecoder.validate_markers() created diagnostics but they were
dropped because StreamDecoder trait doesn't support returning them. Now
diagnostics are emitted in decode_stream_impl() like JBIG2/JPX/CCITT.
Also include source module refactoring:
- Add PdfSource adapter trait for source::PdfSource compatibility
- Feature-gate http_range module with `remote` feature
- Update document.rs to use new source traits
Acceptance criteria:
- DCTDecode emits STREAM_INVALID_JPEG for missing SOI/EOI markers
- JBIG2Decode emits OCR_JBIG2_UNSUPPORTED when full-render disabled
- JPXDecode emits OCR_JPX_UNSUPPORTED and validates JP2 magic
- CCITTFaxDecode emits OCR_CCITT_UNSUPPORTED when no libtiff
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Bead-Id: pdftract-4xmp6
Bead-Id: pdftract-57np8
Bead-Id: pdftract-3954u
