1353e2a29b
Add 9 unit tests covering all demodulators in demod.rs: USB/LSB/Passthrough real-part extraction, AM DC removal and varying-envelope, FM tone frequency and silence, CW peak normalisation, mode mapping, and empty-input safety. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> Signed-off-by: Stan Grams <sjg@haxx.space>