Fix of DeepSeek Error in KV Pool Mixed Deployment Scenario

[fems14]

What this PR does / why we need it?

A new kv_role "kv_both" is added to run mixed deployment scenarios. The mixed deployment will involve a decode phase, where with_prefill should be false.

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.10.2
• vLLM main: vllm-project/vllm@c60e613

[github-actions]

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[gemini-code-assist]

Code Review

This pull request introduces a bugfix for the mooncakestore connector to correctly handle the kv_both role in mixed deployment scenarios. The changes are consistent across the example deployment guide and the core logic in mooncake_engine.py and model_runner_v1.py. The logic to differentiate pure producers from mixed producer/consumer nodes for dummy runs is sound. The updated configurations in the deployment guide align with the code changes. Overall, the changes appear correct and effectively address the issue.