Minor type improvements

[cretz]

What was changed

• Properly support Optional params in workflows/activities
• Make sure that we don't try to send cancelled error to server on worker shutdown (was only caused by the recent Support raising cancellation in sync multithreaded activities #217)
• Updated README to note that generic types are not resolved for purposes of deserialization
• Updated README to properly use asyncio.create_task for calls to asyncio.wait since 3.11 requires that now

Checklist

1. Closes [Bug] Python 3.11 TypeError: Passing coroutines is forbidden, use tasks explicitly. #232
2. Closes [Bug] Generic Nested Dataclasses not desrialized correctly #234
3. Closes [Bug] Optional[X] type not being handled properly as parameter #236
4. Closes [Bug] Activity cancellation error issues #237