Z-Image img2img and inpainting pipeline

### Model/Pipeline/Scheduler description

I have written and opened a PR for implementation of img2img pipeline for Z-Image.

#12751

### 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

_No response_

Start by reading the implementation PR referenced as #12751 and the Z-Image pipeline context in this issue. Done means the proposed img2img and inpainting pipeline implementation is complete and integrated for Z-Image; coordinate with the existing PR rather than starting separate work.

索引モデルが issue の本文から書いたものです。