[Bugfix][WideEP] Apply TP Attn + EP MoE fix to other models

[tlrmchlsmth]

Purpose

Prior to this PR, in many cases, using TP Attn and EP MoEs with --tensor-parallel-size N --data-parallel-size M --enable-expert-parallel would result in factor N redundant work in the MoE layers.

This PR extends #24134 to other models, and to the naive and allgather_reducescatter All2All backends.

Test Plan

vllm serve {{MODEL}} -tp 2 -dp 2 --enable-expert-parallel --port 8192

lm_eval --model local-completions --tasks gsm8k --model_args model={{MODEL}},base_url={{BASE_URL}}/v1/completions,num_concurrent=50,max_retries=3,tokenized_requests=False --limit 100

Test Result

Qwen/Qwen3-30B-A3B-FP8:

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value|   |Stderr|
|-----|------:|----------------|-----:|-----------|---|----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  | 0.88|±  |0.0327|
|     |       |strict-match    |     5|exact_match|↑  | 0.94|±  |0.0239|

Qwen/Qwen3-Next-80B-A3B-Instruct (with --enforce-eager due to #25437):

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value|   |Stderr|
|-----|------:|----------------|-----:|-----------|---|----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  | 0.80|±  |0.0402|
|     |       |strict-match    |     5|exact_match|↑  | 0.74|±  |0.0441|

meta-llama/Llama-4-Scout-17B-16E:

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value|   |Stderr|
|-----|------:|----------------|-----:|-----------|---|----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  | 0.82|±  |0.0386|
|     |       |strict-match    |     5|exact_match|↑  | 0.82|±  |0.0386|

ibm-granite/granite-4.0-tiny-preview (with --enforce-eager due to #25437 (comment)):

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value|   |Stderr|
|-----|------:|----------------|-----:|-----------|---|----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  | 0.58|±  |0.0496|
|     |       |strict-match    |     5|exact_match|↑  | 0.55|±  |0.0500|

openai/gpt-oss-20b (main at TP4 is almost the same):

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.3685|±  |0.0133|
|     |       |strict-match    |     5|exact_match|↑  |0.2365|±  |0.0117|

---

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.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[mergify]

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

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