[BUG]: Fix hint timers continuing to count while hints are being viewed

[seanlip]

This issue is opened to track a part of #4492 that was not fixed in #4500, namely, pausing the hint timer while hints are being viewed. From the original issue:

Hints should appear one by one after a certain amount of time has elapsed. When the user is in the Hint Modal, the timer should not be counting. This is because there should be at least some time which the learner can use to think about and apply the suggestions in the hint before we prompt them with a follow-up hint.

We encountered some challenges when trying to fix this originally. Per @BenHenning (see #4500 (comment)):

The main issue is that hints are handled in the domain layer entirely separately from the frontend lifecycle. We almost certainly would need to either somehow provide signal from the frontend when hints are being shown (and not mess this up since it'll break the hints timer), or manage hint state based on the observation of its results (similar to how ExplorationProgressController used to work), but this is difficult and not at all straightforward since hint behaviors are observed through ExplorationProgressController. I suspect we may need the DataProvider dynamic transformation that I'm working on for the beta release in order to even start tackling this issue.

The aim of this issue is to fix this bug. (This is part of the fast-follow items from #4510.)

[BenHenning]

NB: This is actually a bit tricky to fix since we intentionally moved hints & solution tracking state into the domain layer to fix a bunch of problems that can be caused by transient UI state. I think we need some sort of signal passed from the UI to the domain layer on whether the hints are being actively viewed, and whether the app is in the foreground (the latter we already have some solutions for, see #4916).

[ShubhadeepKarmakar]

I want to work on this but I can't get the clarity of this bug. @adhiamboperes @seanlip @kkmurerwa @BenHenning may someone please explain this to me?

[BenHenning]

@seanlip should we only be running the hint timer when the user is actively seeing the state card? It makes sense to pause when the hint dialog is open, but what about other cases such as concept cards linked from the state content where the user might not be actively viewing the state?

[seanlip]

@BenHenning Thanks for checking -- I think there are arguments for going either way on that, so whatever is technically easiest is fine.

If you want a clearer direction, though, then I think I would lean towards leaving the hint timer counting if the user is viewing a concept card, since they might be doing so in order to review the skill before trying the question again (so this feels like "productive time" to me).