Comprehensive API refactoring and documentation improvements for media_controller plugin

[Copilot]

This PR implements a comprehensive refactoring and improvement of the media_controller Flutter plugin, transforming it from a basic implementation into a production-ready package with modern architecture, type safety, and extensive documentation.

🚀 Major Improvements

New Type-Safe API

Introduced MediaControllerManager class that provides:

• Proper initialization and disposal lifecycle management
• Structured error handling with standardized PlatformException codes
• Real-time media state updates through typed streams
• Better resource management and memory leak prevention

final controller = MediaControllerManager();
await controller.initialize();

// Type-safe media updates
controller.mediaUpdates.listen((MediaPlaybackState state) {
  print('Now playing: ${state.title} by ${state.artist}');
  print('Progress: ${state.formattedPosition}/${state.formattedDuration}');
});

// Discover and control sessions
final sessions = await controller.getActiveMediaSessions();
await controller.setCurrentMediaSession(sessions.first.sessionToken);
await controller.play();

Rich Data Models

Added comprehensive typed models replacing raw maps and strings:

• MediaSessionInfo - Structured session metadata with user-friendly display names
• MediaPlaybackState - Complete playback state with formatted time helpers and progress calculation
• PlaybackStatus enum - Type-safe playback states with display names

Enhanced Android Implementation

Improved the native Android code with:

• Structured error responses using standardized error codes (invalid_argument, player_error, etc.)
• Better resource cleanup and lifecycle management
• Proper exception handling and logging guards
• Added missing NotificationListener service for media session discovery

Comprehensive Documentation

• README: Complete rewrite with detailed API reference, usage examples, and troubleshooting
• API Documentation: Every public method and class now has comprehensive doc comments
• Example App: Completely redesigned with modern Material 3 UI, error handling, and better UX
• CHANGELOG: Detailed tracking of all improvements and breaking changes

Backward Compatibility

The legacy MediaController class remains functional but is marked as deprecated, ensuring existing code continues to work while encouraging migration to the improved API.

🔧 Technical Details

Error Handling

Standardized error codes across Dart and Android:

try {
  await controller.play();
} on PlatformException catch (e) {
  switch (e.code) {
    case 'not_initialized':
      // Handle initialization error
    case 'player_error':
      // Handle playback error
  }
}

Resource Management

• Proper cleanup in onDetachedFromEngine to prevent memory leaks
• Automatic callback unregistration when sessions change
• Stream controllers properly disposed to prevent resource leaks

Testing

Added comprehensive test suite covering:

• New MediaControllerManager initialization and lifecycle
• Data model serialization/deserialization
• Error handling scenarios
• Legacy API compatibility

📊 Impact

• 16 files changed with 1,894 additions and 263 deletions
• Type safety - Eliminates runtime errors from incorrect data types
• Better UX - Rich metadata and progress tracking in example app
• Developer Experience - Comprehensive documentation and clear error messages
• Production Ready - Proper error handling, resource management, and testing

This refactoring addresses all the requirements outlined in the original issue while maintaining backward compatibility and following Flutter plugin best practices.

Warning

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