Async monitor decorator makes type checking complex

[kojiromike]

Async monitor decorator makes type checking complex

[szokeasaurusrex]

@kojiromike This indeed appears to be because of how we typed the monitor after the async changes.

The problem is that we have defined the monitor to return Callable[P, Union[R, Awaitable[R]]]. We instead need to add overloads to specify that monitor returns Callable[P, R] when it is passed a Callable[P, R], and that it returns Callable[P, Awaitable[R]] when it receives a Callable[P, Awaitable[R]].

I will work on a fix now. Hopefully, we will have it ready soon!

[kojiromike]

NB this appears to be very similar to the situation reported python/mypy#15520, and largely handled in https://peps.python.org/pep-0742/. (Though I guess only in python ^3.13.0 IIRC?)