[FIX] Field Groups hydration

lib/src/form/src/controller.dart

@@ -131,13 +131,16 @@ class AstromicFormController {
     final key = parentUuid == null ? '${groupId}_manifest' : '${_getParentKey(groupId, parentUuid)}_manifest';
 
     if (!_nodes.containsKey(key)) {
+      // 1. Create the node with the specific List<String> type
       _nodes[key] = AstromicFieldNode<List<String>>(
-        [],
+        <String>[],
         formatter: (v) => v.length.toString(),
-        parser: (v) => [],
+        parser: (v) => <String>[],
       );
     }
-    return _nodes[key] as ValueNotifier<List<String>>;
+
+    final node = _nodes[key];
+    return (node as dynamic) as ValueNotifier<List<String>>;
   }
 
   /// Adds a new instance to a dynamic group, generating a UUID and initializing all schema fields.