perf: overlap MTP final-draft-to-target graph updates.#1962

pjgao wants to merge 6 commits into

xLLM-AI:mainxLLM-AI/xllm:mainfrom

pjgao:perf/npu-mtp-tp2-gaplesspjgao/xllm:perf/npu-mtp-tp2-gaplessCopy head branch name to clipboard