PeRFlow: Piecewise Rectified Flow as Universal Plug-and-Play Accelerator

### Model/Pipeline/Scheduler description

A competitor of LCM-Lora, with higher generation quality and consistency regardless number of steps

Project page: https://piecewise-rectified-flow.github.io/
Github: https://github.com/magic-research/piecewise-rectified-flow/tree/main

### 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

Maybe we can add the new scheduler to Diffusers

Start with the PeRFlow project page and linked model implementation, then compare its scheduler requirements with the existing Diffusers scheduler conventions. The issue names no Diffusers files or tests; done would require a reviewed scheduler addition with validation against the available implementation and weights.

索引モデルが issue の本文から書いたものです。