feat(src/services): add NumLock service and refactor Battery documentation

Add new NumLock service to monitor NumLock LED state changes.
Refactor Battery service documentation and property cache handling.
Update imports to include NumLock.

src/services/__init__.py

@@ -2,6 +2,7 @@ from fabric.audio import Audio  # noqa: F401
 from .battery import Battery  # noqa: F401
 from .brightness import Brightness  # noqa: F401
 from .capslock import CapsLock  # noqa: F401
+from .numlock import NumLock  # noqa: F401
 from .keyboard_layout import KeyboardLayout  # noqa: F401
 from .network import NetworkClient, Wifi, Ethernet  # noqa: F401
 from .mpris import PlayerService, PlayerManager  # noqa: F401