Rework Check-All

[mo8it]

Closes #2394

Reworked the visualization of the check-all progress. Instead of showing the exercise numbers, an exercise is shown with "done" or "pending" after being checked. To see the output, run cargo r -- check-all.

I also removed the manual input c to trigger check-all. It was offered as an option to avoid hitting n multiple times when the state file is out of sync (e.g. user continues on a different machine without syncing the state file). Instead of a manual trigger, check-all is now triggered automatically when the user hits n and the next exercise is done although it was not marked as such. This means that at least one exercise is done and not marked as such and check-all will fix possible others.

Rather orthogonal, but I did it on the way: I added a timeout to all commands in case a user writes a program which does not terminate. Currently, it is set to 30sec. What do you think about that value? @senekor

[senekor]

The timeout for exercises seems reasonable... but practically, how useful are 30 seconds? I expect most people to hit Ctrl+C before that. Making the timeout too tight seems risky, I don't know how long we should expect compilation to take on weak / old hardware... especially considering we want to add exercises with dependencies like tokio.

[mo8it]

We might need to add either a global configuration option or even allow one for every exercise, especially for community exercises. But I would wait for someone to complain :P