Explain state management in Flutter.

Flutter state management approaches:\n\n**Built-in solutions:**\n• setState() - Local widget state\n• InheritedWidget - Share data down tree\n• ValueNotifier - Simple reactive state\n\n**Popular packages:**\n• Provider - Dependency injection and state\n• Bloc - Business logic separation\n• Riverpod - Modern provider alternative\n• GetX - Complete solution\n• MobX - Reactive state management\n\n**Provider example:**\n\nclass Counter extends ChangeNotifier {\n int _count = 0;\n int get count => _count;\n \n void increment() {\n _count++;\n notifyListeners();\n }\n}\n\n// Usage\nConsumer(\n builder: (context, counter, child) {\n return Text('${counter.count}');\n }\n)\n