Fix import paths and test issues

- Fixed test file import paths to point to correct Bloc file locations
- Fixed Bloc file import paths for models (../../../models/models.dart)
- Added explicit type annotations to resolve null safety warnings
- Fixed null safety issues in wishlist_bloc_test.dart
- All 70 tests now passing

bookshelf_flutter/lib/models/app_screen.dart

@@ -0,0 +1,10 @@
+// App screen enum
+enum AppScreen {
+  library,
+  categories,
+  wishlist,
+  settings,
+  details,
+  addBook,
+  scanner,
+}