Allow arbitrary types in model creation by updating config in create_model

Author: coolbeevip

src/mcp/server/fastmcp/utilities/func_metadata.py

@@ -407,7 +407,7 @@ def _create_wrapped_model(func_name: str, annotation: Any, field_info: FieldInfo
     if annotation is None:
         annotation = type(None)
 
-    return create_model(model_name, result=(annotation, field_info), __base__=BaseModel)
+    return create_model(model_name, result=(annotation, field_info), __base__=BaseModel, __config__={"arbitrary_types_allowed": True})
 
 
 def _create_dict_model(func_name: str, dict_annotation: Any) -> type[BaseModel]: