```

feat: add __call__ in field_serializer and update body wait logic

- In g4f/client/stubs.py, add a __call__ method to the field_serializer class that returns the first positional argument.
- In g4f/requests/__init__.py, replace the wait_for call with a while loop that repeatedly evaluates "document.querySelector('body:not(.no-js)')" and sleeps until the element is found.
```

g4f/client/stubs.py

@@ -22,6 +22,8 @@ except ImportError:
     class field_serializer():
         def __init__(self, field_name):
             self.field_name = field_name
+        def __call__(self, *args, **kwargs):
+            return args[0]
 
 class BaseModel(BaseModel):
     @classmethod