[Feature] Staggered batch scheduling for DP+EP

[ApplEOFDiscord]

Motivation

💡 If this PR is a Cherry Pick, the PR title needs to follow the format by adding the [Cherry-Pick] label at the very beginning and appending the original PR ID at the end. For example, [Cherry-Pick][CI] Add check trigger and logic(#5191)

💡 如若此PR是Cherry Pick，PR标题需遵循格式，在最开始加上[Cherry-Pick]标签，以及最后面加上原PR ID，例如[Cherry-Pick][CI] Add check trigger and logic(#5191)

In MoE inference system, requests arrive DP instances at different timepoints, which causes some DP instances make an idle forward, thereby reducing resource utilization and increasing TTFT

Modifications

To mitigate the above issue, we adopt a batching strategy on both scheduler side and engine side, keeping all DP instances as fully utilized as possible

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]

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2 out of 3 committers have signed the CLA.

✅ ApplEOFDiscord
✅ rainyfly
❌ gzz

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 18.70968% with 126 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@e1a9b28). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/engine/common_engine.py	4.21%	90 Missing and 1 partial ⚠️
fastdeploy/worker/worker_process.py	50.00%	20 Missing and 1 partial ⚠️
fastdeploy/engine/sched/resource_manager_v1.py	9.09%	10 Missing ⚠️
fastdeploy/engine/engine.py	0.00%	1 Missing and 1 partial ⚠️
fastdeploy/engine/expert_service.py	50.00%	0 Missing and 1 partial ⚠️
fastdeploy/worker/gpu_model_runner.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
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  Coverage           ?   65.69%           
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  Files              ?      330           
  Lines              ?    41986           
  Branches           ?     6451           
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  Hits               ?    27581           
  Misses             ?    12358           
  Partials           ?     2047           

Flag	Coverage Δ
GPU	65.69% <18.70%> (?)

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