[BugFix][main] Adapted Qwen3-Next-MTP to chunked prefill (#4770)

### 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.

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

Signed-off-by: drslark <[email protected]>
Co-authored-by: Mengqing Cao <[email protected]>

Author: drslark

tests/e2e/multicard/test_qwen3_next.py

@@ -24,7 +24,6 @@
 import os
 from unittest.mock import patch
 
-import pytest
 from modelscope import snapshot_download  # type: ignore
 
 from tests.e2e.conftest import VllmRunner
@@ -64,14 +63,9 @@ def test_models_distributed_Qwen3_NEXT_TP4_FULL_DECODE_ONLY():
         del vllm_model
 
 
-@pytest.mark.skip
+# TODO: Fix the accuary of batch chunked prefill
 def test_models_distributed_Qwen3_NEXT_MTP_TP4_SIMILARITY():
-    example_prompts = [
-        "Hello, my name is",
-        "The president of the United States is",
-        "The capital of France is",
-        "The future of AI is",
-    ]
+    example_prompts = ["Hello, my name is"]
     max_tokens = 20
 
     with VllmRunner(
@@ -115,7 +109,6 @@ def test_models_distributed_Qwen3_NEXT_MTP_TP4_SIMILARITY():
 
 
 # TODO: will conduct accuracy verification after the subsequent version becomes stable
-@pytest.mark.skip
 @patch.dict(os.environ, {"HCCL_BUFFSIZE": "1024"})
 def test_models_distributed_Qwen3_NEXT_W8A8DYNAMIC_WITH_EP():
     example_prompts = [