[BugFix] fix init RequestOutput

[juncaipeng]

Motivation

修复PD 分离下构造RequestOutput错误

Modifications

RequestOutput.from_dict

Usage or Command

无

Accuracy Tests

无

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!

[Copilot]

Pull request overview

此 PR 修复了在 PD（Prefill-Decode）分离场景下构造 RequestOutput 对象时的错误，同时添加了解码资源分配的时间指标记录。

主要变更：

• 修改 RequestOutput.from_dict 方法以安全处理可能缺失或为 None 的 outputs 和 metrics 字段
• 修正了 insert_tasks 中解码资源分配成功时的处理逻辑
• 添加了解码资源请求的开始和完成时间的指标记录

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
fastdeploy/engine/request.py	添加了对 outputs 和 metrics 字段的条件检查，避免在字段缺失时反序列化失败
fastdeploy/engine/common_engine.py	修正了解码资源分配成功时的逻辑分支，添加了 ask_decode_resource_start_time 和 ask_decode_resource_finish_time 指标

关于 PR 描述的建议：

• PR 标题格式正确：使用了 [BugFix] 标签
• 描述中的"修复PD 分离下构造RequestOutput错误"较为简洁，建议补充更详细的背景信息，例如：
  • 什么场景下会出现此问题？
  • 错误的具体表现是什么？
  • 如何复现该问题？
• 建议说明为何需要添加这两个时间指标（ask_decode_resource_start_time 和 ask_decode_resource_finish_time）

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@80efe98). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/engine/request.py	0.00%	8 Missing ⚠️
fastdeploy/engine/common_engine.py	0.00%	4 Missing ⚠️

Additional details and impacted files

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