feat: add UniPC scheduler

[keturn]

This enables the UniPC scheduler added to diffusers 0.13: https://huggingface.co/docs/diffusers/api/schedulers/unipc

[keturn]

…except it doesn't work. It quickly collapses to zero, within the first few steps.

I also tried running with diffusers main to make sure it wasn't huggingface/diffusers#2595 but that didn't seem to make a difference.

the first hunch that's come to mind is something to do with scale_model_input, since that's one way to drive something to zero, but I don't know yet.

[keturn]

UniPC does work with the stock diffusers pipeline.

The scale_model_input hunch wasn't it, as this scheduler doesn't scale there.

scheduler.config looks the same, scheduler.timestamps looks the same...

[patrickvonplaten]

Hmm weird, the do the following schedulers work:

• https://huggingface.co/docs/diffusers/v0.14.0/en/api/schedulers/deis#diffusers.DEISMultistepScheduler
• https://huggingface.co/docs/diffusers/v0.14.0/en/api/schedulers/multistep_dpm_solver
  ? Because UniPC is in exactly the same format as these ones.

[keturn]

Correction: it doesn't collapse to 0, it collapses to NaN. Running at float32 instead of float16 does not prevent it.

As for the other models:

Yep, we've had DPMSolverMultistepScheduler in use for a bit now.

DEIS seems to work more or less fine.

[lstein]

Any progress on this?

[keturn]

superseded by #3388.

(in theory. in practice I'm getting 422: Unprocessable Entity errors with that, but that's a story for another bug report.)