[Bugfix] fix request_id of image generation in api server

[ZJY0516]

Purpose

FIX #1080, using time as request_id can not handle concurrent requests.

Test Plan

import time
import threading
import requests
import traceback

URL = "http://localhost:8000/v1/images/generations"

PAYLOAD = {
    "prompt": "可爱的卡通橘猫，白色背景",
    "n": 1,
    "size": "512x512",
    "response_format": "b64_json",
    "num_inference_steps": 8,
}

CONCURRENCY = 4        # 改成 3 / 4 也能复现
TIMEOUT = 60           # 秒

barrier = threading.Barrier(CONCURRENCY)

def run(i):
    try:
        print(f"[req {i}] ready")
        barrier.wait()   # 👉 保证同时发请求

        start = time.time()
        resp = requests.post(URL, json=PAYLOAD, timeout=TIMEOUT)
        cost = time.time() - start

        print(
            f"[req {i}] DONE status={resp.status_code} "
            f"cost={cost:.2f}s "
            f"resp_len={len(resp.content)}"
        )

    except Exception as e:
        cost = time.time() - start
        print(
            f"[req {i}] ERROR cost={cost:.2f}s "
            f"type={type(e).__name__} "
            f"err={e}"
        )
        traceback.print_exc()


def main():
    threads = []
    for i in range(CONCURRENCY):
        t = threading.Thread(target=run, args=(i,))
        t.start()
        threads.append(t)

    for t in threads:
        t.join()

    print("=== all threads joined ===")


if __name__ == "__main__":
    main()

Test Result

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft.

BEFORE SUBMITTING, PLEASE READ https://github.com/vllm-project/vllm-omni/blob/main/CONTRIBUTING.md (anything written below this line will be removed by GitHub Actions)