Optimize jsonable_encoder to skip building key set when no include/exclude

fastapi/encoders.py

@@ -280,6 +280,8 @@ def jsonable_encoder(
         return None
     if isinstance(obj, dict):
         encoded_dict = {}
+        allowed_keys: set[Any] | None = None
+        if include is not None or exclude is not None:
             allowed_keys = set(obj.keys())
             if include is not None:
                 allowed_keys &= set(include)
@@ -293,7 +295,7 @@ def jsonable_encoder(
                     or (not key.startswith("_sa"))
                 )
                 and (value is not None or not exclude_none)
-                and key in allowed_keys
+                and (allowed_keys is None or key in allowed_keys)
             ):
                 encoded_key = jsonable_encoder(
                     key,