Improve lost frame recovery with partial reconstruction

[unforced]

Problem

Currently, when packet loss is detected, the entire frame is discarded. This is wasteful since partial frames could be recovered.

Location: lib/utils/audio/wav_bytes_util.dart:68-77

if (packetIndex != _lastPacketIndex + 1 ||
    (frameId != 0 && frameId != _lastFrameId + 1)) {
  debugPrint('[WavBytesUtil] Lost frame detected');
  _lastPacketIndex = -1;
  _pending.clear();  // Discards entire frame
  _lostFrameCount++;
  return;
}

Suggested Solution

Implement partial frame recovery:

bool _isRecoverablePacketLoss(int packetIndex, int frameId) {
  // Allow recovery if we're still within the same frame
  return frameId == _lastFrameId && packetIndex > _lastPacketIndex;
}

void storeFramePacket(List<int> packet) {
  // ... existing code ...
  
  if (packetIndex != _lastPacketIndex + 1 ||
      (frameId != 0 && frameId != _lastFrameId + 1)) {
    
    // Try partial recovery
    if (_isRecoverablePacketLoss(packetIndex, frameId)) {
      debugPrint('[WavBytesUtil] Packet loss detected, attempting recovery');
      
      // Fill gap with silence/interpolation
      final missedPackets = packetIndex - _lastPacketIndex - 1;
      for (int i = 0; i < missedPackets; i++) {
        _pending.addAll(List.filled(content.length, 0)); // Silence
      }
      
      _pending.addAll(content);
      _lastPacketIndex = packetIndex;
      _lastFrameId = frameId;
      return;
    }
    
    // Unrecoverable loss - discard frame
    debugPrint('[WavBytesUtil] Unrecoverable frame loss');
    _lastPacketIndex = -1;
    _pending.clear();
    _lostFrameCount++;
    return;
  }
  
  // ... continue normal processing ...
}

Benefits

• Reduces audio data loss
• Better audio quality with gaps instead of complete frame loss
• More resilient to poor BLE connection quality

Trade-offs

• More complex logic
• Requires silence padding or interpolation
• Could introduce artifacts if not done carefully

Priority

Low-Medium - Nice to have, not critical

Related

• Part of PR #8 review feedback
• Related to Improve Opus decoder error handling with frame skipping #13 (Opus error handling)