[REQUEST] Display: idle operations

[SeongGino]

Screen updates currently don't happen unless explicitly commanded to, either by switching to pause mode or by the PC in serial handoff mode. Since the main core isn't doing much between camera polls, we should be able to perform "idle" ops on the display under certain circumstances.

The immediate example that comes to mind is the ability to overlay "RELOAD" text over an empty ammo counter, showing "DAMAGED" or "HIT" text over the life glyphs when damaged for a few seconds, showing a short "GAME OVER" text when exiting serial handoff, and replacing the top ticker text with different information periodically (i.e. #23).

Perhaps we can use the RP2040 PWM timer that we have in use now, so that the decrementer is updated along with the camera enable timer (not saying it has to update AS fast; just that we use the resources we already have that are available to us).