[V1] Support DeepSeek MTP in V1

[WoosukKwon]

🚀 The feature, motivation and pitch

DeepSeek MTP should be ported to the new V1 architecture.

Alternatives

No response

Additional context

No response

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[xiefan46]

Hi @WoosukKwon @sroy745, I am new to the vllm community and trying to find a onboarding task to start with. Seems like this issue hasn't been updated for a long time. May I take this one as my onboarding task?