[BugFix][Cherry-Pick] cp fix dyc8 cache bug(#5958)

[kevincheng2]

Motivation

修复ep + dyc8 + cudagraph 场景，命中部分cache时，请求返回乱码问题

Modifications

1. prefixcache保证命中token数为 block_size 的整数倍
2. 更新metric记录，配置为真实命中token数

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 30.43478% with 16 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/2.4@16645c6). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/engine/sched/resource_manager_v1.py	23.80%	15 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release/2.4    #5959   +/-   ##
==============================================
  Coverage               ?   58.72%           
==============================================
  Files                  ?      329           
  Lines                  ?    40846           
  Branches               ?     6225           
==============================================
  Hits                   ?    23987           
  Misses                 ?    14984           
  Partials               ?     1875           

Flag	Coverage Δ
GPU	58.72% <30.43%> (?)

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