Put modules back on children for wall switches (#881)

Puts modules back on the children for `WallSwitches` (i.e. ks240) and
makes them accessible from the `modules` property on the parent.

kasa/module.py

@@ -4,11 +4,14 @@ from __future__ import annotations
 
 import logging
 from abc import ABC, abstractmethod
+from typing import TYPE_CHECKING
 
-from .device import Device
 from .exceptions import KasaException
 from .feature import Feature
 
+if TYPE_CHECKING:
+    from .device import Device
+
 _LOGGER = logging.getLogger(__name__)