refactor: create separate BLoCs for each screen with comprehensive tests

- Created 8 separate BLoCs (Home, Library, BookDetails, AddBook, Scanner, Categories, Wishlist, Settings)
- Each BLoC has its own event, state, and bloc files
- Added 70 comprehensive tests covering all BLoC functionality
- All tests passing (70/70)
- Fixed linting issues and updated deprecated APIs
- Improved code organization and maintainability

bookshelf_flutter/lib/bloc/settings/settings_event.dart

@@ -0,0 +1,25 @@
+abstract class SettingsEvent {
+  const SettingsEvent();
+}
+
+class LoadSettings extends SettingsEvent {
+  const LoadSettings();
+}
+
+class UpdateTheme extends SettingsEvent {
+  final bool isDarkMode;
+  const UpdateTheme(this.isDarkMode);
+}
+
+class UpdateLanguage extends SettingsEvent {
+  final String language;
+  const UpdateLanguage(this.language);
+}
+
+class ToggleNotifications extends SettingsEvent {
+  const ToggleNotifications();
+}
+
+class ClearData extends SettingsEvent {
+  const ClearData();
+}