feat: port Atomic

[markusdemedeiros]

Description

Depends on #659, merge that first

I am very unsure about the notations section. It more or less has to be written for the files depending on this, but I am not confident in my ability to review the generated code. Please be extra critical of this section.

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.