[NIXL] vllm v0 nixl integration

[rainj-me]

Features are supported in this PR

• vllm v0 nixl integration without etcd/nats as dependencies
• http apis to handshake nixl conns
• MLA layout support
• MTP and speculative decoding support
• Remote prefill worker skip sampling to reduce TTFT

Usage scripts

# Decode worker
vllm serve /data/models/QwQ-32B --tensor_parallel-size 2 --port 8080 --max-model-len 131072 --swap-space 0  --block-size 128 --trust-remote-code --kv-transfer-config '{"kv_connector":"DynamoNixlConnector"}' --enable-chunked-prefill false

# Remote prefill worker
vllm serve /data/models/QwQ-32B --tensor_parallel-size 1 --port 8090 --max-model-len 65536 --swap-space 0  --block-size 128 --gpu-memory-utilization 0.95 --trust-remote-code --enforce-eager --kv-transfer-config '{"kv_connector":"DynamoNixlConnector", "kv_connector_extra_config":{"skip_sampling":true}}' --enable-chunked-prefill false

# Establish nixl conn
curl -kvvv -XPOST http://127.0.0.1:8080/add_remote_prefill_eps  -H "Content-Type: application/json" -d '{"endpoints":["http://127.0.0.1:8090"]}'

# Test command
curl http://127.0.0.1:8080/v1/chat/completions -H "Content-Type: application/json" -d '{"model": "/data/models/QwQ-32B", "temperature": 0, "messages": [ {"role": "user", "content": "San Francisco is "}], "max_tokens": 300, "stream": false}'

What are left

1. chunked-prefill support
2. PP support
3. vllm V1 support
4. Only keep DynamoNixlConnector and cleanup other connectors

[github-actions]

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @rainj-me.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @rainj-me.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork