[BugFix] Fix accuracy problem in dp situation.

[whx-sjtu]

This PR is a quick fix of the accuracy problem mentioned in PR #1856.

• vLLM version: v0.10.0
• vLLM main: vllm-project/vllm@004203e

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[MengqingCao]

It seems the implement of dispatch and combine is same as that in NaiveAll2AllManager, I think we'd better to call these communication ops through NaiveAll2AllManager, like #1856 does, instead of coping them here.

[wangxiyuan]

yes, if nothing changed with NaiveAll2AllManager, we should import from vllm directly instead of copy the code.

[whx-sjtu]

Got it, I will change this soon.

[MengqingCao]

Got it, I will change this soon.

To avoid duplicated work, I think #1856 is enough, and I'm working on adding accuracy test on dp + moe.

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This pull request has conflicts, please resolve those before we can evaluate the pull request.