[KVCache] launch cache transfer processes only if hierarchical cache or kv cache storage is enabled

[liyonghua0910]

Motivation

当前在开启 PrefixCaching 时，会伴随启动一个 CacheTransferManager 进程，用于 CPU-GPU 的缓存块交换，以及外部缓存存储的读写，而该进程并非 PrefixCaching 所需。

Modifications

• 修改 CacheTransferManager 进程的启动条件为，开启 CPU Cache 或 KV Cache Storage 时才启动。
• 同步修改了 clear/update 接口的判断逻辑

Usage or Command

Accuracy Tests

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
  • You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!

[codecov-commenter]

Codecov Report

❌ Patch coverage is 29.41176% with 24 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@e911ac2). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/entrypoints/engine_client.py	0.00%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #5871   +/-   ##
==========================================
  Coverage           ?   66.61%           
==========================================
  Files              ?      347           
  Lines              ?    44412           
  Branches           ?     6824           
==========================================
  Hits               ?    29587           
  Misses             ?    12639           
  Partials           ?     2186           

Flag	Coverage Δ
GPU	66.61% <29.41%> (?)

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