Add comprehensive tests for Omi BLE services

[unforced]

Problem

Current test coverage (27 tests) only covers models and validators. Missing tests for critical BLE functionality:

• BLE connection logic
• Audio packet assembly
• Codec conversion (PCM8/16, Opus)
• Platform-specific behavior
• Error recovery scenarios

Suggested Test Files

Create the following test suite:

test/services/omi/
├── omi_bluetooth_service_test.dart
├── omi_connection_test.dart
├── omi_capture_service_test.dart
├── wav_bytes_util_test.dart
└── platform_utils_test.dart

Example Tests

1. omi_bluetooth_service_test.dart

group('OmiBluetoothService', () {
  test('should discover devices during scan', () async { ... });
  test('should connect to device by ID', () async { ... });
  test('should handle disconnection', () async { ... });
  test('should auto-reconnect to paired device', () async { ... });
});

2. wav_bytes_util_test.dart

group('WavBytesUtil - Frame Assembly', () {
  test('should assemble multi-packet frames correctly', () { ... });
  test('should handle lost frames gracefully', () { ... });
  test('should decode Opus frames to PCM', () { ... });
  test('should build valid WAV header', () { ... });
});

3. omi_capture_service_test.dart

group('OmiCaptureService', () {
  test('should start recording on button event', () async { ... });
  test('should save recording with correct metadata', () async { ... });
  test('should handle codec selection', () async { ... });
});

Mocking Strategy

Use mocktail for mocking BLE dependencies:

dev_dependencies:
  mocktail: ^1.0.0

Benefits

• Catch regressions early
• Document expected behavior
• Enable confident refactoring
• Improve code quality

Priority

Medium - Important for long-term maintainability

Related

• Part of PR #8 review feedback
• See dev-docs/suggested-testing.md for testing philosophy