bail out of upload type checks early for strs

Signed-off-by: technillogue <technillogue@gmail.com>

python/cog/json.py

@@ -47,6 +47,9 @@ def upload_files(obj: Any, upload_file: Callable[[io.IOBase], str]) -> Any:
 
     When a file is encountered, it will be passed to upload_file. Any paths will be opened and converted to files.
     """
+    # skip four isinstance checks for fast text models
+    if type(obj) == str:  # noqa: E721
+        return obj
     if isinstance(obj, dict):
         return {key: upload_files(value, upload_file) for key, value in obj.items()}
     if isinstance(obj, list):