feat: support PD disaggregation

[ma-hang]

Summary

• 支持 PD 分离推理服务，打通了 prefill 与 decode 节点之间的 KV cache 传输、调度协同、服务路由和异常恢复流程，使系统能够在分离部署场景下完成请求转发、远端预填充、KV 复用与后续解码。

Motivation

• support PD disaggregation

Type of Change

• feat — new feature / new model
• fix — bug fix
• perf — performance improvement (no behavioral change)
• refactor — code restructuring without behavior change
• test — adding or fixing tests only
• docs — documentation only
• build / ci — build system or CI configuration
• chore — tooling, formatting, or other non-code changes
• Breaking change

Test Results of Involved Models on Supported Platforms (Please attach screenshots)

Benchmark / Performance Impact

Notes for Reviewers

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Testing

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[ma-hang]

NVIDIA(1P1D) - MiniCPM-V-2_6

NVIDIA(1P1D) - 9g_8b_thinking