[Feature] Add check health in FD

[rainyfly]

Motivation

防止 token processor hang 死，添加探活接口由于探知。

Modifications

新增服务层探活 check 项：token processor组件

Usage or Command

None

Accuracy Tests

None

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

This PR adds health monitoring functionality for the token processor to detect and prevent hang situations. The implementation introduces a health check command that can be called externally to verify if the token processor is operating correctly.

Key changes:

• Added healthy() method to check token processor health status based on timestamp tracking
• Implemented timestamp monitoring before and after batch processing
• Added check_health command handler in the internal adapter

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 7 comments.

File	Description
fastdeploy/envs.py	Adds FD_TOKEN_PROCESSOR_HEALTH_TIMEOUT configuration with 120-second default
fastdeploy/output/token_processor.py	Implements health monitoring with timestamps and healthy() method to detect hung states
fastdeploy/splitwise/internal_adapter_utils.py	Adds check_health command handler that invokes the token processor's healthy() method

[codecov-commenter]

Codecov Report

❌ Patch coverage is 20.00000% with 20 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@12c76f8). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/output/token_processor.py	26.31%	14 Missing ⚠️
fastdeploy/splitwise/internal_adapter_utils.py	0.00%	6 Missing ⚠️

Additional details and impacted files

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  Partials           ?     1890           

Flag	Coverage Δ
GPU	60.73% <20.00%> (?)

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