Expose hooks for external audio drivers

[kshoji]

Summary

Fix double audio callback 53efa8f

• Add useBuiltInAudioFilter on ChuckMainInstance / ChuckSubInstance so callers can disable OnAudioFilterRead when another path advances the shared VM (avoids double ManualAudioCallback / double UGen reads).
  • The default behavior around OnAudioFilterRead is unchanged.

Add Read-only accessors for some private fields

• Expose Main mic state via GetMicClip() / GetMicDevice(). fb48ab5
• Expose Sub replacement-DAC name and running status via OutputUgen / IsRunning. bc488bf

Motivation

Integrations such as Unity 6 Scriptable Audio Generators need to drive ChucK from outside OnAudioFilterRead. Currently, the required state is private, so consumers must use reflection.