Some of these unwraps are fine to stay, mostly those that deal with
locks - in this case, crashing the program if something goes wrong is
probably fine.

However, we also had a lot of other places where we panic'd on errors,
even though we really shouldn't have. For example, an invalid zip file
would bring down the whole scanner. In this case, we now use proper
Result<>s and we log the error.

Some places stay with unwrap() for now, mainly the code that is rare and
obvious when it goes wrong - such as an overflow in input values. It
could be made nicer, but it is not a priority for now.

Some unwraps() have been changed to expect() to signal why they
shouldn't fail.

There's a good chance that this will be evtclib 0.5, so we want to adapt
our API usage (mainly replacing evtclib::Boss with evtclib::Encounter).

The naming is a bit all over the place now, as we sometimes refer to
bosses and sometimes to encounters, but I hope to make a sensible
decision at *some point* about what we're actually doing here.

Since we have this information now anyway, might as well include it.
We're using humantime here, as that produces the expected "xxm yys zzms"
output. The conversion shouldn't fail (the unwrap), as we should never
encounter negative fight durations.