Integrate LaVie (IJCV 2024) and Cinemo (CVPR 2025) to diffusers

### Model/Pipeline/Scheduler description

I am one of the authors of LaVie (IJCV 2024) and Cinemo (CVPR 2025). We are considering submitting pull requests (PRs) to the diffusers repository for these two video models, both of which are based on U-Net architectures. We would like to know if `diffusers` is still open to supporting PRs for U-Net-based models. If so, we will proceed with the submissions. 

### Open source status

- [x] The model implementation is available.
- [x] The model weights are available (Only relevant if addition is not a scheduler).

### Provide useful links for the implementation

LaVie:  [Vchitect/LaVie: [IJCV 2024] LaVie: High-Quality Video Generation with Cascaded Latent Diffusion Models](https://github.com/Vchitect/LaVie)
Cinemo: [maxin-cn/Cinemo: [CVPR 2025] Cinemo: Consistent and Controllable Image Animation with Motion Diffusion Models](https://github.com/maxin-cn/Cinemo)

Empieza leyendo las implementaciones enlazadas de LaVie y Cinemo y comparando su estructura de modelo con las expectativas de contribución de diffusers. Primero hay que confirmar que se admiten los modelos basados en U-Net; se considerará completado cuando exista un plan de integración acordado y posteriormente se creen pull requests para ambos modelos.

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