These focus on the public API with the private aspect omitted. This is
because these are hard to type, and may not be required with modern
python. However, this should still be useful if adopted for code
that uses blinker.

This allows for signals to send to coroutine receivers by awaiting
them. The _async_wrapper and _sync_wrapper allows for conversion of
sync and async receivers as required if defined. If not defined a
runtime error is raised.

The wrappers are used to avoid any direct tie into asyncio, trio,
greenbacks, asgiref, or other specific async implementation.

This allows int values as senders much in the same way string values
are allowed.

This is useful whilst testing to remove a signal's affects.

Co-authored-by: Michael Elovskikh <wronglink@yandex-team.ru>