[Cherry-Pick][Feature] consider multimodal model when dummy run(#6045)

[kevincheng2]

Motivation

dummy_run支持多模动态切 chunk（实际推理token有可能会超过chunk_size限制），避免多模态模型分配 block_num 过多导致OOM

Modifications

1. data_processor 增加 get_mm_max_tokens_per_item 方法，计算每个模态数据的最大token数
2. dummy_run chunk 最大token数统一使用 get_max_chunk_tokens 方法获取

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 96.00000% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/2.4@603aab0). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/config.py	85.71%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release/2.4    #6349   +/-   ##
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  Coverage               ?   56.31%           
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  Files                  ?      333           
  Lines                  ?    42280           
  Branches               ?     6431           
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  Hits                   ?    23811           
  Misses                 ?    16606           
  Partials               ?     1863           

Flag	Coverage Δ
GPU	56.31% <96.00%> (?)

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