Arcade-BASIC

Implement audio output support with SOUND, BEEP, and PLAY statements; add BufferedAudioDevice for PCM streaming in Unity.

Add tests for audio statements: SOUND, BEEP, and PLAY

Document unsupported MML commands and add tests for variable pointer rejection

Implement real-time audio playback and background music support

Implement audio extension with SOUND, BEEP, and PLAY statements