[WIP] [Entrypoints] add video online serving

[david6666666]

PLEASE FILL IN THE PR DESCRIPTION HERE ENSURING ALL CHECKLIST ITEMS (AT THE BOTTOM) HAVE BEEN CONSIDERED.

Purpose

Test Plan

vllm serve Wan-AI/Wan2.2-T2V-A14B-Diffusers --omni --port 8093 --cache-backend cache_dit

curl -s http://localhost:8093/v1/chat/completions   -H "Content-Type: application/json"   -d '{
    "messages": [
      {"role": "user", "content": "A curious raccoon"}
    ],
    "extra_body": {
      "height": 480,
      "width": 640,
      "num_frames": 80,
      "fps": 16,
      "num_inference_steps": 40,
      "guidance_scale": 4.0,
      "guidance_scale_2": 3.0,
      "seed": 42
    }
  }' | jq -r '.choices[0].message.content[0].video_url.url' | cut -d',' -f2 | base64 -d > output.mp4

Test Result

output.mp4

---

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)