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/test/bloc/settings/settings_bloc_test.dart

@@ -0,0 +1,105 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:bookshelf_flutter/bloc/settings/settings_bloc.dart';
+import 'package:bookshelf_flutter/bloc/settings/settings_event.dart';
+import 'package:bookshelf_flutter/bloc/settings/settings_state.dart';
+
+void main() {
+  group('SettingsBloc', () {
+    late SettingsBloc settingsBloc;
+
+    setUp(() {
+      settingsBloc = SettingsBloc();
+    });
+
+    tearDown(() {
+      settingsBloc.close();
+    });
+
+    test('initial state is SettingsState.initial()', () {
+      expect(settingsBloc.state, isA<SettingsState>());
+      expect(settingsBloc.state.isLoading, true);
+    });
+
+    group('LoadSettings', () {
+      test('loads default settings into state', () async {
+        settingsBloc.add(const LoadSettings());
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.isDarkMode, false);
+        expect(settingsBloc.state.language, 'English');
+        expect(settingsBloc.state.notificationsEnabled, true);
+        expect(settingsBloc.state.isLoading, false);
+      });
+    });
+
+    group('UpdateTheme', () {
+      test('updates isDarkMode to true', () async {
+        settingsBloc.add(const UpdateTheme(true));
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.isDarkMode, true);
+      });
+
+      test('updates isDarkMode to false', () async {
+        settingsBloc.add(const UpdateTheme(true));
+        await Future.delayed(Duration.zero);
+
+        settingsBloc.add(const UpdateTheme(false));
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.isDarkMode, false);
+      });
+    });
+
+    group('UpdateLanguage', () {
+      test('updates language setting', () async {
+        settingsBloc.add(const UpdateLanguage('Russian'));
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.language, 'Russian');
+      });
+
+      test('updates language to English', () async {
+        settingsBloc.add(const UpdateLanguage('English'));
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.language, 'English');
+      });
+    });
+
+    group('ToggleNotifications', () {
+      test('toggles notifications from true to false', () async {
+        settingsBloc.add(const LoadSettings());
+        await Future.delayed(Duration.zero);
+        expect(settingsBloc.state.notificationsEnabled, true);
+
+        settingsBloc.add(const ToggleNotifications());
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.notificationsEnabled, false);
+      });
+
+      test('toggles notifications from false to true', () async {
+        settingsBloc.add(const UpdateTheme(false));
+        await Future.delayed(Duration.zero);
+        settingsBloc.add(const ToggleNotifications());
+        await Future.delayed(Duration.zero);
+        expect(settingsBloc.state.notificationsEnabled, false);
+
+        settingsBloc.add(const ToggleNotifications());
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.notificationsEnabled, true);
+      });
+    });
+
+    group('ClearData', () {
+      test('sets dataCleared to true', () async {
+        settingsBloc.add(const ClearData());
+        await Future.delayed(Duration.zero);
+
+        expect(settingsBloc.state.dataCleared, true);
+      });
+    });
+  });
+}