Prevent assignments of FX modules to model

[pablomlago]

Reason for this PR

When replacing a module by a RotatedModule in fused_rotation_no_fx via a ModuleInstanceToModuleInstance rewriter, a tying between the model and its FX counterpart is created, as the replaced module in the model will point to a RotatedModule which, itself, points to module of the FX model. This is an inconsistency which is problematic when registering parametrizations, for instance.

Changes Made in this PR

Create a new type of rewriter for wrapping a module with a new class, which, itself, contains an instance to the original module. This rewriter is less general than ModuleInstanceToModuleInstance, but it is more transparent for this specific use-case.

Testing Summary

To be added.

Risk Highlight

• This PR includes code from another work (please detail).
• This PR contains API-breaking changes.
• This PR depends on work in another PR (please provide links/details).
• This PR introduces new dependencies (please detail).
• There are coverage gaps not covered by tests.
• Documentation updates required in subsequent PR.

Checklist

• Code comments added to any hard-to-understand areas, if applicable.
• Changes generate no new warnings.
• Updated any relevant tests, if applicable.
• No conflicts with destination dev branch.
• I reviewed my own code changes.
• Initial CI/CD passing.
• 1+ reviews given, and any review issues addressed and approved.
• Post-review full CI/CD passing.

[pablomlago]

This could be solved alternatively by reassigning the attribute "layer" in RotatedModule in fix_rewriters to point to the updated old_module_instance. I chose to implement a different rewriter as it feels more transparent.