feat: implement polling-based headphone detection with software debounce

[DavidMenting]

Summary

Replaces hardware auto-detect with direct MFP3 pin reading and time-based software debouncing for headphone jack detection. This provides better control over detection behavior and centralizes policy logic in the AudioOutput HAL layer.

Driver Layer Changes (Aic3204)

• Read MFP3 pin state directly from GPIO control register (Page 0, Reg 0x36) instead of hardware auto-detect result register
• Remove hardware auto-detect initialization from init() (Page 0, Reg 0x43 setup)
• Remove update_headphone_detection() method that embedded policy logic in the driver
• Remove _headphone_inserted_state member variable

HAL Layer Changes (AudioOutput)

• Implement time-based software debouncing (20ms poll interval, 75ms debounce duration)
• Add debounce state machine with SDK time functions (get_absolute_time(), absolute_time_diff_us())
• Cache debounced state and notify listeners only on confirmed state changes
• Add new public API:
  • headphones_inserted() - Returns cached debounced state
  • set_headphone_listener() - Register callback for state changes
  • clear_headphone_listener() - Clear callback
  • enable_auto_speaker_mute() - Toggle automatic amp control policy

Architecture Benefits

• Clean separation: driver provides semantic read API, HAL orchestrates polling and policy
• Codec-agnostic: application layer accesses headphone state through AudioOutput
• Configurable: poll interval and debounce duration via build-time constants
• Testable: policy and debouncing logic isolated from hardware I/O

Test Plan

• Verify headphone insertion/removal detected on hardware within ~75-95ms
• Confirm no false triggers from contact bounce
• Test auto-mute policy correctly toggles external amp
• Verify listener callbacks invoked on debounced state changes only
• Check no audible artifacts during amp toggling