[Graph Optimization][Speculative Decoding] Fix the bug of CUDAGraph + MTP + EP

[gongshaotian]

Motivation

When used in CUDAGraph+MTP+EP scenarios, Draft Models on different GPUs may run empty, causing all_gather() to receive an error when obtaining step_use_cudagraph.

Origin PR: #4456

Modifications

Draft Model directly uses the step_use_cudagraph Flag of Target Model

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]]
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• 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!