[Chore] Add some optimization rules

Side note: DROP n ; DROP would work by the same principle, but the issue with that is we'd need KnownList constraint on DROP's input, and that one's used extensively in a lot of places, some of those aren't trivial to extend with the constraint.

Description

Problem: While working on another project (context), we found some optimization rules are missing. Those with proofs (or not requiring proofs) can be added to morley.

Solution: Add those rules. Some PeanoSing utilities were needed, so those are added as well. One caveat is that DIG now requires KnownList constraint on its input.

Related issue(s)

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