Can pass level without typing all possible keys

[shiblon]

It is currently possible to pass a level without typing all of the keys within it. That should probably be fixed.

One thing that makes this nontrivial is the fact that superlevels have a lot of keys represented in them. Testing out, for example, might involve a lot of typing. We could initially just enforce the "all keys hit" criterion on leaf levels, but that is not entirely satisfying.

Mastery is what matters for testing out, so it's probably a good idea to change the approach there, but it is not clear what is practical.