Strip ITU-R M.493 phasing symbols (120-126) after dot pattern sync before
decoding message content. Fix MMSI BCD digit trimming direction and correct
test symbol encodings for position and MMSI edge cases.
- Add parser tests for MMSI country lookup, distress codes, format codes
- Add decoder tests for MMSI/position decoding, bit conversion
- Add database tests for DSC alerts CRUD operations
- Include constants validation tests
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>