[RFC] More robust revert functions for convergence tests

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### 🐛 Describe the bug

Many discussions show that the current revert functions have several limitations, including:

- incomplete revert: https://github.com/linkedin/Liger-Kernel/pull/627#issuecomment-2757281103 #542
- not automatically updating old reference: #385
- comparing wrong references: https://github.com/linkedin/Liger-Kernel/pull/627#issuecomment-2756914629

Simply reloading the modules would generate new class/function objects different from the original ones, i.e. `revert(patch(object)) != object`, which can easily lead to bugs when doing comparisons (`isinstance()`), repatching, reusing configs and so on.

One way to address the issue is having a patch manager for testing to keep track of replaced objects, so we can easily revert back to the original objects after monkey patch. Or is there a way to achieve it with pytest?

cc @tyler-romero @austin362667

### Reproduce

_No response_

### Versions

none

Start with the current revert functions used by the convergence tests, then review the linked discussions in PR #627 and issues #542 and #385. Define a testing approach that preserves original object identity, updates old references, and compares the correct references; done means these listed limitations are covered by reproducible tests.

Written by the indexing model from the issue text.