feat: finish CMRA.lean

[markusdemedeiros]

Description

Finish a bunch of CMRA lemmas.

Only thing I really noticed on review was that Rocq uses Empty_set. This PR aliases it to a the Lean type Empty... they're both empty inductive types, and Empty_set seems to serve the same purpose, but it's also stated as this strange Ensemble thing so I'm not 100%.

Checklist

• My code follows the mathlib naming and code style conventions
• I have added my name to the authors section of any appropriate files

Generative AI Guidelines

AI assistance is permitted when making contributions to Iris-Lean, however, generative AI systems tend to produce code which takes a long time to review.
Please carefully review your code to ensure it meets the following standards.

• Your PR should avoid duplicating constructions found in Iris-Lean or in the Lean standard library.
• have statements that do not aid readability or code reuse should be inlined.
• Your proofs should be shortened such that their overall structure is explicable to a human reader. As a goal, aim to express one idea per line.
• In general, proofs should not perform substantially more case splitting than their Rocq counterparts.

In our experience, a good place to begin refactoring is by re-arranging and combining independent tactic invocations.
We also find that pointing generative AI systems to the Mathlib code style guidelines can help them perform some of this refactoring work.

[markusdemedeiros]

NOTE: Duplicated in #617. Delete before merging if gmap wins the race.