Add fast prescale option to upscaler settings (off by default)

[LoganBooker]

Description

By default, upscaling will loop several times to upscale incoming images to the target dimensions. This is necessary, as upscaling models work in fixed increments (x4 is common). However, for very small images, such as those generated by ADetailer for inpainting, this can regularly result two upscaling steps. The second step is often expensive, far exceeding the target dimensions, and is particularly wasteful as it will be forcibly downsized by the final part of the upscale method anyway.

Examining the behaviour, it's often the case that a minor resize using Lanczos before the upscaling loop would guarantee a single upscaling step that hits or slightly exceeds the target dimensions.

This commit introduces an optional value to the upscaler settings allowing this minor resize, should the incoming image fall below a certain threshold compared to the fixed scaling value of the upscaling model. By default, this setting is set to 1.0, disabling it. Values of 1.25-3.0 are recommended.

Screenshots/videos:

N/A

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests

[light-and-ray]

Also it's useful to add an option to select upscaler for this last step. For example this one is instant and I would like to use it for this 4x-Nomos8k-span-otf-medium

[light-and-ray]

But I can't give a simple suggestion. Because in this implementation import recursion is unavoidable. I think it's better to move this prescale_threshold feature from Upscaler class into resize_image function. Also it's kinda more logically