feat: enable EPLB for NVFP4 compressed-tensors ML3 checkpoint

[hypdeb]

Purpose

Allow enabling eplb for the NVFP4 MoE compressed-tensors path.

Also, fix Mistral Large 3 not being recognized as an MoE model.

In the process, the following additional changes were made:

• Use types to make the three possible EPLB state of the router explicit: no state (EPLB is disabled), uninitialized state (EPLB is enabled, but the state is not initialized), initialized state (EPLB is initialized and state is initialized).
• Make router the owner of EPLB state
• Added missing pytest markers (benchmark, fork)

Test Plan

Testing end-to-end with EPLB enabled.

Test Result

TODO

[gemini-code-assist]

Code Review

This pull request enables EPLB for NVFP4 compressed tensors and fixes an issue where Mistral Large 3 was not recognized as a Mixture-of-Experts model.

The changes in vllm/model_executor/layers/fused_moe/router/base_router.py to relax EPLB state validation during initialization and in vllm/model_executor/layers/quantization/compressed_tensors/compressed_tensors_moe.py to enable EPLB support for NVFP4 are correct and well-implemented.

In vllm/model_executor/models/pixtral.py, the changes correctly proxy the MoE interface from the underlying language model. However, the current implementation of copying attributes is fragile and could lead to stale state. I've suggested a more robust approach using @property decorators to ensure the wrapper always reflects the true state of the language model.

[ilmarkov]

Don't we check the same in _validate_eplb_state? Do the asserts make sense if we do the same readiness check? Maybe we need to return readiness flag in validate and actuall skip EPLB mapping until eplb state is ready

[hypdeb]

I've adjusted the modelling of EPLB state in the router to be more explicit, which removes the needs for these asserts. There are now three possible states: None, uninitialized, initialized.

[hypdeb]

Scope of changes is larger. I will test and mark the PR as ready when it's done.

[hypdeb]

While testing, discovered that the PR is effectively blocked by: #32564. Without it, I would have to add some hacks.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @hypdeb.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork