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/home/home_event.dart

@@ -0,0 +1,14 @@
+import '../../models/models.dart';
+
+abstract class HomeEvent {
+  const HomeEvent();
+}
+
+class LoadHomeData extends HomeEvent {
+  const LoadHomeData();
+}
+
+class NavigateToScreen extends HomeEvent {
+  final AppScreen screen;
+  const NavigateToScreen(this.screen);
+}