[Cherry-Pick][BugFix] cp iamge revert bug(#6061)

[kevincheng2]

Motivation

修复两个边界case：

1. 当cache刚好命中图片起始位置的token时，请求会hang在 revert_chunked_mm_input 方法中
2. 当切chunk刚好切到图片起始位置时，会丢失图片信息

Modifications

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 20.00000% with 4 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/online/20251131@c8e882f). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/engine/sched/resource_manager_v1.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##             release/online/20251131    #6066   +/-   ##
==========================================================
  Coverage                           ?   56.76%           
==========================================================
  Files                              ?      324           
  Lines                              ?    39392           
  Branches                           ?     5945           
==========================================================
  Hits                               ?    22360           
  Misses                             ?    15221           
  Partials                           ?     1811           

Flag	Coverage Δ
GPU	56.76% <20.00%> (?)

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