[Feature][EPLB] Add support for unquantized models

[hsliuustc]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

This PR aims to work with the long term todo with this PR: #18343
Add EPLB support for unquantized MoE model,

Test Plan

GPUs: 4 * A100-80G

vllm serve /workspace/models/DeepSeek-V2-Lite \
  --gpu-memory-utilization 0.85 \
  --tensor-parallel-size 4 \
  --enforce-eager  \
  --host 0.0.0.0 \
  --port 20001 \
  --enable-eplb \
  --enable-expert-parallel \
  --trust-remote-code \

curl -X POST http://127.0.0.1:20001/v1/completions  \
     -H "Content-Type: application/json" \
     -d '{
         "model": "/workspace/models/DeepSeek-V2-Lite",
         "prompt": ["Explain the theory of relativity in simple terms."],
         "max_tokens": 50,
         "temperature": 0.0,
         "top_p": 1,
         "top_k": 1
         }'

Test Result

(Optional) Documentation Update

[gemini-code-assist]

Code Review

This pull request adds support for Expert Parallelism Load Balancing (EPLB) to unquantized Mixture of Experts (MoE) models, which is a great enhancement. The changes look good overall.

My main feedback is on the use of assert statements for input validation in vllm/model_executor/layers/fused_moe/layer.py. While assert is useful for internal sanity checks, it's not suitable for validating parameters in library code because assertions can be disabled in production environments. I've suggested replacing them with explicit checks that raise ValueError or TypeError to make the code more robust.

Please take a look at my detailed comments. Thanks for the contribution!

[github-actions]

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[mergify]

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

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

[abmfy]

It looks like EPLB support for unquantized models has been implemented in #20775. Could you please confirm if that’s the case?
Thanks again for the contribution!