Enhancement: hide the device preview / correct key for a few seconds

[Groxx]

The request
As much as I like having the device preview on-screen for learning characters as a beginner (CC1), it quickly becomes a crutch rather than a learning tool. Sorta like looking down at your hands when learning to touch-type, but even easier to "cheat" since you can somewhat figure out the highlight without even looking away from the input field.

Describe the solution you'd like
Some option (perhaps even the default) to hide the device preview / correct key / known keys once you appear to "know" a key, until it seems like you need the hint.

I'd probably take it in a few stages, which would also fit options that could be presented:

1. Just hide the whole preview container for like 3 seconds (renewing after each press). If they can't find the key within those 3 seconds, they might need the hint. Personally I'd also try to detect frustration (say 3 wrong presses 200ms+ apart, to ignore mashing / bad chords) and show it faster.
2. Always show the keyboard, but don't highlight the correct key until ^ that time passes.
3. Hide "known" keys, and maybe do a two-phase appear-then-highlight with ^ those timeouts. This way you'd always see keys that you haven't learned, giving you more chances to absorb them passively.

And all of these can get arbitrarily fancy in trying to figure out "good" timings, e.g. lengthen it as you appear to learn a key better, or don't hide it at all until you've hit the key correctly 10x, or something something spaced repetition something, etc. I don't see much harm in starting out dumb though, and it might even be good enough to stop there.

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I might be interested in building number 1 since I suspect it'd be pretty simple for a new-to-this-codebase person. Beyond that I really have no idea. And I would not mind in the least if someone else builds it, I'm unfortunately pretty constantly busy and might not get around to it :(