fix(shared): prevent loading more when reaching bottom while extracting

- Add a check for loading state before triggering onLoadMore()
- Extract isLoadingExtractor from widget to avoid redundant calls
- Improve performance and prevent unnecessary API calls

Author: fulleni

lib/shared/widgets/searchable_dropdown_form_field.dart

@@ -141,7 +141,8 @@ class _SearchableSelectionDialogState<T, B extends BlocBase<S>, S>
   }
 
   void _onScroll() {
-    if (_isBottom) {
+    final isLoading = widget.isLoadingExtractor(widget.bloc.state);
+    if (_isBottom && !isLoading) {
       widget.onLoadMore();
     }
   }
@@ -228,4 +229,4 @@ class _SearchableSelectionDialogState<T, B extends BlocBase<S>, S>
       },
     );
   }
-}
+}