Correct modulation parameters (1200 bps, 2100/1300 Hz tones), replace
invented format codes with the six ITU-defined specifiers {102, 112,
114, 116, 120, 123}, accept all valid EOS symbols (117, 122, 127),
add parser validation (format, MMSI, raw field, telecommand range),
and fix truthiness bugs that dropped zero-valued fields.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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.