[Feature] Support Unipic 3.0 Pipeline

**Is your feature request related to a problem? Please describe.**
Yes. Currently, there is no native pipeline in diffusers that supports Unified Multi-Image Conditioning as proposed in UniPic 3.0. https://huggingface.co/Skywork/Unipic3

**Describe the solution you'd like.**
I propose adding a UniPic 3.0–style pipeline to diffusers that natively supports multi-image, multi-type conditioning within a single diffusion forward pass.

**Describe alternatives you've considered.**
Extending existing pipelines: Results in model-specific hacks rather than a reusable abstraction. And it's difficult to maintain or generalize.

**Additional context.**
Add any other context or screenshots about the feature request here.

Inizia esaminando la pagina del modello UniPic 3.0 collegata nell’issue e i pattern esistenti delle pipeline di diffusers. Definisci come deve funzionare il conditioning multi-immagine e multi-tipo all’interno di un singolo forward pass di diffusione. Il lavoro sarà completato quando diffusers fornirà una pipeline nativa e riutilizzabile in stile UniPic 3.0, invece di estensioni specifiche del modello.

Scritto dal modello di indicizzazione a partire dal testo della issue.