Make custom EventfulDigitialOutputDevice class with callback functions so leds can turn on/off automatically

[fergusL]

Ideally all these LED operations should be done automatically by when_activated & when_deactivated callback functions associated with the relays. Unfortunately the gpiozero DigitalOutputDevice class doesn't have those attributes like DigitalInput does. But! We could fairly easily fix that oversight by making out own DigitalOutputDevice subclass that includes the EventsMixin though... I think it would be a simple as:

from gpiozero import DigitalInputDevice, DigitalOutputDevice
from gpiozero.mixins import EventsMixin

class EventfulDigitalOutputDevice(EventsMixin, DigitalOutputDevice):
    pass

Multiple inheritance is powerful magic...

Originally posted by @AnthonyHorton in https://github.com/_render_node/MDE3OlB1bGxSZXF1ZXN0UmV2aWV3Mjk1OTgyODEx/pull_request_reviews/more_threads

[fergusL]

Have tried the above but the callback functions do not seem to get activated by the DigitalOutputDevice.on() calls used to switch the relay positions. Probably need to do a little bit more poking around to figure out what's going on