feat: Adds hires fix on layer diffusion

[db0]

• feat: Adds hires fix to layer diffusion
• fix: Ensures steps are used as intended in stable cascade
• chore: Adds pipeline design for layer diffusion on standard SD
• fix: Uses denoise to calculate a lower step count when doing hires fix second pass
  • Previous to this change, hires fix was doing the full amount of steps on each pass. This is unnecessary as there are (massive) diminishing returns on the second pass.
    • For example, 10 steps versus 20 steps on the second pass can be virtually indistinguishable from each other, so this logic will ultimately help reduce the time spent generating these images. This is especially true for high-step requests.
  • It is worth pointing out that the reference images used to confirm images remain the same version-to-version of horde-engine did not require updating. These images are checked using a form of cosine similarity, so at least to the computer, the 'new' generated hires fix images are basically identical before and after the change.

All tox passes on my end

[db0]

@tazlin I added a change which sets the upscale steps to 30% of the normal steps. From what I see, this doesn't change the results by any significant amount so that could be a good workaround and later we can expose the hires_steps as well. Can you validate as well?

[tazlin]

Everything looks reasonable as of now. Assuming tests pass, I'm OK with a rebase onto main and publishing for a (at least brief) beta testing window with workers.

[tazlin]

@tazlin I added a change which sets the upscale steps to 30% of the normal steps. From what I see, this doesn't change the results by any significant amount so that could be a good workaround and later we can expose the hires_steps as well. Can you validate as well?

I just wanted to emphasize that the images are visually identical to my eye and did not require updating/changing for the cosine image similarity/histogram checks.