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/add_book/add_book_event.dart

@@ -0,0 +1,27 @@
+
+abstract class AddBookEvent {
+  const AddBookEvent();
+}
+
+class InitializeForm extends AddBookEvent {
+  final Map<String, dynamic>? prefilledData;
+  const InitializeForm(this.prefilledData);
+}
+
+class UpdateFormField extends AddBookEvent {
+  final String field;
+  final dynamic value;
+  const UpdateFormField(this.field, this.value);
+}
+
+class ToggleFavorite extends AddBookEvent {
+  const ToggleFavorite();
+}
+
+class ClearForm extends AddBookEvent {
+  const ClearForm();
+}
+
+class SubmitBook extends AddBookEvent {
+  const SubmitBook();
+}