Remove callback from cosmoaudio API

Using callbacks is still problematic with cosmo_dlopen() due to the need
to restore the TLS register. So using callbacks is even more strict than
using signal handlers. We are better off introducing a cosmoaudio_poll()
function. It makes the API more UNIX-like. How bad could the latency be?

dsp/audio/cosmoaudio/Makefile.msvc

@@ -3,6 +3,7 @@
 #     nmake /f Makefile.msvc check
 #     nmake /f Makefile.msvc MODE=debug check
 #
+# Note: MSVC 2019 makes the DLL 64kb smaller than MSVC 2022.
 
 # Compiler and linker
 CC=cl