[Cherry-Pick] [BugFix] fix num_cpu_blocks computation (#6438)

[liyonghua0910]

Motivation

修复 num_cpu_blocks 计算错误问题：

• 在此 PR 之前，若要分配 100G 内存用作 cpu cache，需要配置 swap_space: 50；
• 在此 PR 之后，若要分配 100G 内存用作 cpu cache，需要配置 swap_space: 100。

Modifications

见 "Files changed".

Usage or Command

--swap-space 指定每个实例需要分配用作 cpu blocks 的内存大小 (单位 GB)

Accuracy Tests

无

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 95.65217% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/2.5@574d15f). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/cache_manager/cache_transfer_manager.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release/2.5    #6473   +/-   ##
==============================================
  Coverage               ?   68.52%           
==============================================
  Files                  ?      391           
  Lines                  ?    52728           
  Branches               ?     8209           
==============================================
  Hits                   ?    36134           
  Misses                 ?    13972           
  Partials               ?     2622           

Flag	Coverage Δ
GPU	68.52% <95.65%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.