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/iot/iotdevice.py

@@ -18,8 +18,9 @@ import collections.abc
 import functools
 import inspect
 import logging
+from collections.abc import Mapping, Sequence
 from datetime import datetime, timedelta, timezone
-from typing import TYPE_CHECKING, Any, Mapping, Sequence, cast
+from typing import TYPE_CHECKING, Any, cast
 
 from ..device import Device, WifiNetwork
 from ..deviceconfig import DeviceConfig

kasa/iot/modules/lightpreset.py

@@ -2,8 +2,9 @@
 
 from __future__ import annotations
 
+from collections.abc import Sequence
 from dataclasses import asdict
-from typing import TYPE_CHECKING, Optional, Sequence
+from typing import TYPE_CHECKING, Optional
 
 from pydantic.v1 import BaseModel, Field