[Bug] finalize_shutdown hangs on workflow only worker

[cretz]

Describe the bug

Attempting to update Python SDK to latest core. If I have a workflow-only worker (doesn't even have to do anything), when I initiate_shutdown(), then I properly get the poll shutdown error, then when I finalize_shutdown() it hangs.

[cretz]

Debugging shows that this only occurs when you don't set no_remote_activities to true (i.e. when there are no activities at all and you never poll). The reason TS doesn't suffer from this is because they don't properly wait on finalize.

[Sushisource]

Closing since this behavior is expected in the event that flag isn't set. The contract lang is expected to follow is either to set that flag, in which case it may not poll activities - or to always poll for activities until both poll types return shutdown, then finalize can proceed.

Reason being, if the flag isn't set, there may very well be remote activity tasks which were polled for an accepted by the worker, and I have no choice but to drop them on the floor when finalizing. Hence it is better to state that lang must poll in that situation, so that tasks may be handled if any exist.