Replace empty dict literal with built-in dict function

Description: Performance optimization. Replacing the dict() calls with direct {} statements

fastapi/utils.py

@@ -76,7 +76,7 @@ def create_cloned_field(
 ) -> ModelField:
     # _cloned_types has already cloned types, to support recursive models
     if cloned_types is None:
-        cloned_types = dict()
+        cloned_types = {}
     original_type = field.type_
     if is_dataclass(original_type) and hasattr(original_type, "__pydantic_model__"):
         original_type = original_type.__pydantic_model__