asyncio.sleep()
Closes #7866. This adds an overload to `asyncio.sleep()`, so that when it is called _without_ `return=None`, the type checker knows that the return type is `None` instead of `unknown`. Also related to https://github.com/microsoft/pyright/issues/3475.
collections.abc
asyncio.coroutines.__all__
Future._callbacks
@property
asyncio.selector_events.__all__