[BugFix] fix work metrics not returned by metrics api

[liyonghua0910]

Motivation

当前的 metrics 接口，只返回了 main_process_metrics 的信息，而没有返回 work_process_metrics 中包含的指标。排查到是因为 PROMETHEUS_MULTIPROC_DIR 环境变量的设置晚于 work_process_metrics 的实例化导致的，work_process_metrics 中的指标没有以多进程的模式被初始化，从而 multiprocess.MultiProcessCollector 没有到收集相关信息。

Modifications

将环境变量 PROMETHEUS_MULTIPROC_DIR 的初始化提前到 fastdeploy/__init__.py 文件中，这样通过 python -m fastdeploy.entrypoints.openai.api_server 启动服务时立即初始化该环境变量。

Usage or Command

python -m fastdeploy.entrypoints.openai.api_server \
    --model baidu/ERNIE-4.5-0.3B-Paddle \
    --port 8580 \
    --metrics-port 8581 \
    --engine-worker-queue-port 8582 \
    --cache-queue-port 8583 \
    --max-model-len 65536

Accuracy Tests

$ curl -X POST "http://0.0.0.0:8580/v1/completions" -H "Content-Type: application/json" -d '{
  "prompt": "鲁迅是谁"
}'
{"id":"cmpl-67fb8a8d-3f03-464c-b9a3-ef97ecd8e89e","object":"text_completion","created":1762757964,"model":"/root/PaddlePaddle/ERNIE-4.5-0.3B-Paddle","choices":[{"index":0,"text":"？\n\nA.阿基米德\nB.巴比伦人\nC.伊拉克人\nD.埃及人\n\n请解答这个问题。\n\n**答案**：A.阿基米德\n\n**解析**：阿基米德是古希腊数学家、哲学家，被认为是西方数学和哲学之父，是古希腊“三贤”之一。","prompt_token_ids":null,"completion_token_ids":null,"prompt_tokens":null,"completion_tokens":null,"arrival_time":null,"logprobs":null,"draft_logprobs":null,"reasoning_content":null,"finish_reason":"stop","tool_calls":null}],"usage":{"prompt_tokens":2,"total_tokens":80,"completion_tokens":78,"prompt_tokens_details":{"cached_tokens":0,"image_tokens":null,"video_tokens":null},"completion_tokens_details":{"reasoning_tokens":0,"image_tokens":0}}}

$ curl -i http://0.0.0.0:8581/metrics | grep prompt_tokens_total
# HELP fastdeploy:prompt_tokens_total Total number of prompt tokens processed
# TYPE fastdeploy:prompt_tokens_total counter
fastdeploy:prompt_tokens_total 2.0

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 71.42857% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@b9bdf82). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/__init__.py	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #4912   +/-   ##
==========================================
  Coverage           ?   59.73%           
==========================================
  Files              ?      317           
  Lines              ?    38683           
  Branches           ?     5815           
==========================================
  Hits               ?    23106           
  Misses             ?    13750           
  Partials           ?     1827           

Flag	Coverage Δ
GPU	59.73% <71.42%> (?)

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.