Make diagnostics module visible to fingerprint module and fix
hash_page_geometry signature to match usage.
Changes:
- Add `pub mod diagnostics;` to lib.rs for module visibility
- Modify hash_page_geometry to create diagnostics internally
The canonicalize module already has complete implementation:
- canonicalize_f64: banker's rounding to 4dp for geometry
- normalize_content_stream: whitespace normalization via lexer
- serialize_dict_canonical: sorted-key dict serialization
- hash_resource_dict_canonical: order-independent resource hashing
Verification: notes/pdftract-154mz.md
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
