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/device.py

@@ -106,9 +106,10 @@ from __future__ import annotations
 
 import logging
 from abc import ABC, abstractmethod
+from collections.abc import Mapping, Sequence
 from dataclasses import dataclass
 from datetime import datetime
-from typing import TYPE_CHECKING, Any, Mapping, Sequence
+from typing import TYPE_CHECKING, Any
 from warnings import warn
 
 from typing_extensions import TypeAlias