[Bug] Optional[X] type not being handled properly as parameter

[cretz]

Describe the bug

Our check at

sdk-python/temporalio/common.py

Line 247 in 1f72c98

if not inspect.isclass(arg_hint) or arg_hint is inspect.Parameter.empty:

that does inspect.isclass is False for typing.Optional (which is an alias for typing.Union). Remove that check. And make sure to write a test accepting an optional parameter (ideally using a Pydantic model as the inner optional value since this is what was originally reported).