Native PUSA Support

### Feature Idea

https://huggingface.co/RaphaelLiu/Pusa-Wan2.2-V1

Regarding ComfyUI compatibility: Pusa-Wan2.2 isn’t natively supported in ComfyUI just yet. For I2V support within ComfyUI, I’d recommend checking out Kj’s integration of the Pusa pipeline for Wan2.1. I think he’s implemented support for I2V via a custom [scheduler](https://github.com/kijai/ComfyUI-WanVideoWrapper/blob/42d71807590b42e518f9f5065d9f69e2d8eba81d/wanvideo/schedulers/flowmatch_pusa.py#L5) and shared a helpful [example](https://github.com/kijai/ComfyUI-WanVideoWrapper/issues/804#issuecomment-3089426576).

As for why WanImageToVideo nodes aren’t working: Pusa uses a vectorized timestep paradigm, where we directly set the first timestep to zero (or a small value) to enable I2V (the condition image is used as the first frame). This differs from the mainstream approach, so existing nodes may not handle it.

(from this discussion: https://huggingface.co/RaphaelLiu/Pusa-Wan2.2-V1/discussions/3)

### Existing Solutions

Use custom nodes.