[Doc][Misc] Update DreamID-Omni Example; Add DreamID-Omni post process function

[yuanheng-zhao]

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Purpose

When adding support for diffusion optimization features, it took me quite a while to successfully run DreamID-Omni...

This PR is a partial generation cleanup and example use case adding, so that users could follow the added example use case and run more quickly.

This PR

1. Added post process function to DreamID-Omni pipeline (for vllm-omni consistency), so that we could unpack pipeline output with metadata.
2. Updated DreamID-Omni example usage - Added a single-IP (oneip) usage example
3. Updated generation script to use vllm-omni's mux_video_audio_bytes to save video

TODO:
For now, the model weights and some dependency files are downloaded and installed by examples/offline_inference/x_to_video_audio/download_dreamid_omni.py, which downloads dependency repo and manually write to environment - this seems not to be elegant and convenient to use. I think we still need to refactor this way of installing dependency in future.

Test Plan

# Example usage for oneip, ref media from the official repo DreamID-Omni
python x_to_video_audio.py \
  --model /path/to/dreamid_omni \
  --prompt "<img1>: In the frame, a woman with black long hair is identified as <sub1>.\n**Overall Environment/Scene**: A lively open-kitchen café at night; stove flames flare, steam rises, and warm pendant lights swing slightly as staff move behind her. The shot is an upper-body close-up.\n**Main Characters/Subjects Appearance**: <sub1> is a young woman with thick dark wavy hair and a side part. She wears a fitted black top under a light apron, a thin gold chain necklace, and small stud earrings.\n**Main Characters/Subjects Actions**: <sub1> tastes the sauce with a spoon, then turns her face toward the camera while still holding the spoon, her expression shifting from focused to conflicted.\n<sub1> maintains eye contact, swallows as if choosing her words, and says, <S>I keep telling myself I’m fine,but some nights it feels like I’m just performing calm.<E>" \
  --image-path 9.png \
  --audio-path 9.wav \
  --video-negative-prompt "jitter, bad hands, blur, distortion" \
  --audio-negative-prompt "robotic, muffled, echo, distorted" \
  --cfg-parallel-size 2 \
  --num-inference-steps 45 \
  --height 704 \
  --width 1280 \
  --output out_dreamid_omni_oneip.mp4

Test Result

out_dreamid_omni.mp4

---

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• The test plan. Please provide the test scripts & test commands. Please state the reasons if your codes don't require additional test scripts. For test file guidelines, please check the test style doc
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[yuanheng-zhao]

PTAL @Bounty-hunter , @SamitHuang