feat(prover): WitnessGenerator refactoring #2

[Artemka374]

What ❔

Introduce WitnessGenerator trait
Rename some methods

Why ❔

Checklist

• PR title corresponds to the body of PR (we generate changelog entries from PRs).
• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• Code has been formatted via zk fmt and zk lint.

[EmilLuta]

Overall LGTM. Left a bunch of nits. Here's 1 not very popular opinion:
I believe we can have a single binary for all witness generators (except basic -- and it may include proof compressor as well), because they mostly do the same thing, just load slightly different artifacts & operate on different tables.

Basic Witness Generator is different (because it's not really a witness generator anyways, it runs the VM and does a lot of other things alongside).

Whilst I don't think we should change the approach in this PR, I'd think about it. This setup is already better than what we had before, but I'm super positive we can get away with a minimal amount of custom code for leaf/node/rt/scheduler.

[Artemka374]

Actually I beliebe we really can do it the way that Leaf/node/rt/scheduler have the minimum amount of different code and I think much more changes can be done on this field, but I want to do these changes step by step(to not break anything). But yes, I think we can do something like that in the next PRs