anduril: move candle mode to loop()

[Selene ToyKeeper]

Candle mode's logic is implemented inside its event handler. This works, but it means it's locked at 62 fps. I'd like to move the logic to the inside of loop() instead, to clean up an already-cluttered event handler and make it easier to adjust parameters like the frame rate.

On a related note, it might also be a good idea to break out parts of loop() into their own functions, if it can be done without increasing the ROM size. It has gotten pretty cluttered too.