type annotate the tests (using monkeytype and manual fixes)

[graingert]

• Fixed the type annotation of open_signal_receiver() as a synchronous context manager
• Fixed the type annotations of AsyncFile.__aiter__, readline, write to also accept/return str
  and also fixed AsyncFile.writelines to take an Iterable[str|bytes] rather than bytes.
• Fixed DeprecatedAwaitable(|List|Float).__await__ to match the typing.Awaitable protocol

[graingert]

this will need a history with the user facing type changes

[agronholm]

Do we really need that many annotation changes in the library itself? Did the typed tests reveal that many issues?

[graingert]

Do we really need that many annotation changes in the library itself? Did the typed tests reveal that many issues?

Technically the backends didn't need changes to _SignalReciever because the type information gets destroyed by get_asynclib.

Also fileio only needed __aiter__ changing but I fixed the other bytes only methods

But other than that everything came from mypy errors

[graingert]

this as_path was unused

[agronholm]

Then perhaps we should add this?

        if not as_path:
            socket_path = str(socket_path)

[graingert]

I fixed it at runtime by making a Union[str, Path] fixture

[graingert]

Because you can't reassign a Path to a str, in refactoring it to a fixture I noticed the bug in the test

[agronholm]

Comments, questions and a few change requests.

[agronholm]

Thanks!