Async Scheduling X Spec Decoding Compatibility

[jesse996]

What this PR does / why we need it?

this PR is based on PR vllm-project/vllm#24799 ,and aims to support spec decode with async_scheduling.
and fix crash in Eagle Speculative Decoding models when the input length exceed the drafter model length but not the verifier's based on pr vllm-project/vllm#24662

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.11.2
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

[github-actions]

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[gemini-code-assist]

Code Review

This pull request introduces support for speculative decoding with asynchronous scheduling on Ascend NPUs. The changes are primarily within vllm_ascend/worker/model_runner_v1.py, modifying the model execution and token sampling logic to handle the new asynchronous speculative decoding path. While the overall approach seems reasonable, my review has identified several critical issues that need to be addressed. These include a logic error that nullifies the speculative decoding output processing, duplicated code blocks, and incorrect usage of CUDA-specific stream APIs instead of the appropriate NPU APIs for the Ascend platform. There is also a syntax error that appears to be a merge artifact. These issues will prevent the code from functioning correctly and must be fixed.