Add code to do color compositing on inpainting

[willhsmit]

This is intended as a fix for #597, which might take some further iteration.

Adds a UI parameter under 'Init Image' called 'Color Correction Behavior' with values 'None', 'Uniform', and 'Linear'.

• None is the default and is intended as a noop from current
• Uniform implements the behavior from https://discord.com/channels/1243166023859961988/1243185862234210389/1327390619068530729: find the mean difference between source and dest for each of HSV and apply it to source.
• Linear attempts to model the dest as a linear function of source and apply the function to source. Experimentally, I found that Hue is rarely improved and sometimes made a lot worse by correction, and decided to leave Hue uncorrected. Typically, the derived function will increase the saturation and contrast of the image somewhat.

You mentioned putting it behind a parameter; I assume you meant a UI parameter and not a server/user parameter that hides the UI parameter - I didn't see a lot of prior art for that but am open to fixing it.

I left the Uniform method as an option since I think the Linear option is not always better than it and people may want to experiment. I mostly left the code for Uniform as it was in the discord, but am open to:

• Trying the same removal of Hue as Linear
• Removing the .remainder() from the clamp at the end. I took this out of Linear because it sometimes produces black spots in the middle of a bright white. This happens occasionally but less often in Uniform; I wasn't sure if the remainder() was in there for an important reason.

[mcmonkey4eva]

The parameter should be... somewhere else. Honestly not sure where, maybe shoved under Advanced Sampling?

Because it's needed for <segment: usage especially, not just init image.
That or both an init image one, and a Regional Prompting one.

[willhsmit]

The parameter should be... somewhere else. Honestly not sure where, maybe shoved under Advanced Sampling?

Because it's needed for <segment: usage especially, not just init image. That or both an init image one, and a Regional Prompting one.

I can't think of a better spot for the parameter than Advanced Sampling; I put it under some VAE-related parameters.

I tried doing some segment tests, the seam and the correction effect are pretty subtle. I'll add a couple to the bug thread.

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I ended up removing remainder() and also Hue from the 'Uniform' algorithm; there are some pretty clear examples from testing where those made things worse.