test: add unit tests for poultry repository and searchable dropdown functionalities

- Introduced tests for `PoultryScienceRepositoryImp` to validate delegated remote calls.
- Added comprehensive tests for `SearchableDropdownLogic` covering selection, overlay, and search logic.
- Enhanced `SearchableDropdown` widget tests for multi-select, label building, and overlay management.

lib/presentation/pages/system_design/system_design.dart

@@ -12,17 +12,6 @@ class SystemDesignPage extends StatefulWidget {
 class _SystemDesignPageState extends State<SystemDesignPage> {
   List<bool> _isOpen = [false, false, false, false, false, false];
 
-  void _handleAdd() {
-    print("Add FAB pressed");
-  }
-
-  void _handleEdit() {
-    print("Edit FAB pressed");
-  }
-
-  void _handleDelete() {
-    print("Delete FAB pressed");
-  }
 
   @override
   Widget build(BuildContext context) {