Add internal utility to log audio streams to disk from real-time audio callbacks

[padenot]

I'll expose this to rust next. Example usage in test_audio_dump.cpp.

This is going to be quite useful to diagnose exactly what comes out of the system level callbacks, and compare to what is resampled and delivered at the application level, etc.

@Pehrsons

[padenot]

This seems to be working well from my testing.