[Cherry-Pick] [KVCache] launch cache transfer processes only if hierarchical cache or kv cache storage is enabled (#5871)

[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。而负责 CPU-GPU 的缓存交换的进程只是在开启 CPU Cache 时才需要，而非 PrefixCaching 所需。

Modifications

• 修改 CacheTransferManager 进程的启动条件为，开启 CPU Cache 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 0% with 34 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/2.4@2a71e42). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/entrypoints/engine_client.py	0.00%	24 Missing ⚠️
fastdeploy/cache_manager/prefix_cache_manager.py	0.00%	8 Missing and 2 partials ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release/2.4    #5859   +/-   ##
==============================================
  Coverage               ?   58.86%           
==============================================
  Files                  ?      329           
  Lines                  ?    40773           
  Branches               ?     6209           
==============================================
  Hits                   ?    24003           
  Misses                 ?    14895           
  Partials               ?     1875           

Flag	Coverage Δ
GPU	58.86% <0.00%> (?)

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