[BugFix][main] Adapted Qwen3-Next-MTP to chunked prefill

[drslark]

What this PR does / why we need it?

The pad -1 modification is from vllm-project/vllm#25743.

It still has bugs for batched chunked prefill.

So, we just let e2e to be right.

pytest -s tests/e2e/multicard/test_qwen3_next.py::test_models_distributed_Qwen3_NEXT_MTP_TP4_SIMILARITY

Outputs:

========================================================================================================================== warnings summary ===========================================================================================================================
../../usr/local/python3.11.10/lib/python3.11/site-packages/torch_npu/dynamo/torchair/__init__.py:8
  /usr/local/python3.11.10/lib/python3.11/site-packages/torch_npu/dynamo/torchair/__init__.py:8: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
    import pkg_resources

<frozen importlib._bootstrap>:241
  <frozen importlib._bootstrap>:241: DeprecationWarning: builtin type SwigPyPacked has no __module__ attribute

<frozen importlib._bootstrap>:241
  <frozen importlib._bootstrap>:241: DeprecationWarning: builtin type SwigPyObject has no __module__ attribute

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
============================================================================================================== 1 passed, 3 warnings in 172.17s (0:02:52) ==============================================================================================================

Does this PR introduce any user-facing change?

N/A

How was this patch tested?

• vLLM version: v0.12.0
• vLLM main: vllm-project/vllm@ad32e3e

[gemini-code-assist]

Code Review

This pull request adapts the Qwen3-Next-MTP model for chunked prefill, primarily by adding a fallback implementation for causal convolution and enabling the corresponding tests. The changes also include patches to work around limitations in torch_npu and vLLM's utility functions.

My review focuses on the maintainability and risks associated with these workarounds. While the changes appear to be functional for the immediate goal, they introduce significant technical debt:

1. A large block of code for causal convolution has been duplicated from upstream, which will be difficult to maintain.
2. Two separate monkey patches are introduced for bind_kv_cache and torch.argsort. These are risky and can lead to future breakages.

I've added comments with high severity for these issues, recommending the creation of tracking issues to address the underlying problems and eventually remove these temporary solutions. These measures are crucial for the long-term health of the codebase.

[github-actions]

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[wangxiyuan]

Remove Discussed with @MengqingCao

[wangxiyuan]

move to patch module

[wangxiyuan]

rename to patch_qwen3_next