[torch.compile] Speed up MOE handling in forward_context

[zou3519]

Purpose

This is a follow up to the comments on
#32805 .

It contains the following two perf optimizations:

• We don't need to recompute all of the MOE layer names on every forward pass. Instead we can get all of the layer names when the model is being initialized
• Stop popping strings from a list. Instead, maintain a counter.

Test Plan & Test Result

I tested this locally. Compilation time remains good while models still produce reasonable results. Also, wait for CI.

[gemini-code-assist]

Code Review

The pull request successfully implements two performance optimizations for MOE handling: pre-computing MOE layer names during model initialization and using a counter-based approach instead of popping from a list in the ForwardContext. The changes are well-aligned with the stated purpose and appear to be correctly implemented across the affected files. The refactoring improves efficiency by reducing redundant computations and list manipulations during the forward pass. No critical or high-severity issues were found.