Improve shared Led interface for smart devices

The current implementation of the time interface doesn't address the way the led works for plugs which is that the led on-state is a read only property, the led on-state when the rule `always` is enabled is on when the device is on and off when it is off.

N.B. This does not seem to be the case for wall switches, e.g. ks240.

Reference: https://github.com/python-kasa/python-kasa/pull/1002