[Cherry-Pick][BugFix] Fix eplb weight updating(#5529)

[RichardWooSJTU]

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)

Modifications

Reason: Unfinished dp rank would not be detected, which let worker process of dp0 send reload signal.

Fix: Add unfinished detection.

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 14.28571% with 6 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/online/20251131@f133ce5). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/eplb/experts_manager.py	14.28%	6 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##             release/online/20251131    #5661   +/-   ##
==========================================================
  Coverage                           ?   59.16%           
==========================================================
  Files                              ?      319           
  Lines                              ?    39091           
  Branches                           ?     5887           
==========================================================
  Hits                               ?    23130           
  Misses                             ?    14115           
  Partials                           ?     1846           

Flag	Coverage Δ
GPU	59.16% <14.28%> (?)

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.