### What this PR does / why we need it?
This PR rebases RecomputeScheduler codebase to vllm tags/v0.14.1 in
order to fix the incompatibility with vllm's original Scheduler and
AsyncScheduler. Main changes focus on multimodal model and speculative
decoding parts.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
We tested this PR with 2P1D E2E serving test case.
- vLLM version: v0.14.1
- vLLM main:
d68209402d
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Signed-off-by: linfeng-yuan <1102311262@qq.com>