Drop python3.8 support (#992)

Drop support for soon-to-be eol'd python 3.8.
This will allow some minor cleanups & makes it easier to add support for
timezones.

Related to
https://github.com/python-kasa/python-kasa/issues/980#issuecomment-2170889543

kasa/discover.py

@@ -86,7 +86,8 @@ import binascii
 import ipaddress
 import logging
 import socket
-from typing import Awaitable, Callable, Dict, Optional, Type, cast
+from collections.abc import Awaitable
+from typing import Callable, Dict, Optional, Type, cast
 
 # When support for cpython older than 3.11 is dropped
 # async_timeout can be replaced with asyncio.timeout