refactor: optimize providers with keepAlive for improved state management

- Updated multiple providers to use `@Riverpod(keepAlive: true)` for better state retention throughout the app lifecycle.
- Enhanced `SocketConnectionStream` and `ConversationDeltaStream` with comments clarifying the purpose of public getters.
- Improved error handling in the `_ChatPageState` by ensuring proper checks for mounted state before using context.
- Added comments to clarify the rationale behind keepAlive usage in various providers, ensuring better maintainability and understanding of the codebase.

lib/core/services/settings_service.dart

@@ -407,7 +407,7 @@ bool _listEquals(List<String> a, List<String> b) {
 }
 
 /// Provider for app settings
-@riverpod
+@Riverpod(keepAlive: true)
 class AppSettingsNotifier extends _$AppSettingsNotifier {
   bool _initialized = false;