Add debug log on audio start/stop.
Do not run playback test in ctest.

Indicates segfault for some reason under ctest, manually works ok.
sim_transmit test doesn’t actually work.

The simulator runs to completion before first rtaudio callback is ever
called.
Some noisy debug logging.
Enable send and receive chains in both cases (incoming and outgoing).

The final protocol will need to be changed to actually send commands
triggering send and receive behavior.
Bump submodules.