fix: mark _deprecate_threads_param as a wrapper to unblock introspection and docs (#1122)

Author: andrewsg

google/cloud/storage/transfer_manager.py

@@ -22,6 +22,7 @@
 import warnings
 import pickle
 import copyreg
+import functools
 
 from google.api_core import exceptions
 from google.cloud.storage import Client
@@ -61,6 +62,7 @@
 
 
 def _deprecate_threads_param(func):
+    @functools.wraps(func)
     def convert_threads_or_raise(*args, **kwargs):
         binding = inspect.signature(func).bind(*args, **kwargs)
         threads = binding.arguments.get("threads")