Remove support for python <3.11 (#1273)

Python 3.11 ships with latest Debian Bookworm. 
pypy is not that widely used with this library based on statistics. It could be added back when pypy supports python 3.11.

kasa/transports/xortransport.py

@@ -18,12 +18,9 @@ import errno
 import logging
 import socket
 import struct
+from asyncio import timeout as asyncio_timeout
 from collections.abc import Generator
 
-# When support for cpython older than 3.11 is dropped
-# async_timeout can be replaced with asyncio.timeout
-from async_timeout import timeout as asyncio_timeout
-
 from kasa.deviceconfig import DeviceConfig
 from kasa.exceptions import KasaException, _RetryableError
 from kasa.json import loads as json_loads