Blocking call scheduled on loop when closing connection

[mvn23]

When the serial connection is closed or lost, _call_connection_lost() is scheduled on the loop from _abort() or _close(). From there, _serial.close() is called here:

pyserial-asyncio/serial_asyncio/__init__.py

Line 417 in 44d4701

self._serial.close()

Unfortunately, _serial.close() calls time.sleep(0.3) in certain cases (e.g. here), which blocks the entire loop for its duration.

See also: home-assistant/core#67430 where the problem was first mentioned.

[elupus]

Should be enough to run close, and probably open in an asyncio executor.