FEAT: Factor out upscaling into a separate node

[tildebyte]

Is there any way to make this more "Comfy"?

I'll note up front that this is similar to #9

RE: Fig. 3 from the paper, "(a) Starting with conventional resolution generation"; i.e., instead of a monolithic node which replaces literally all of ComfyUI[1], it'd be nice to have a node which could take a generated "normal-sized" image or latent (whichever is required; I'm not completely certain on that point) from an existing workflow, and run it through the DemoFusion process...

IOW "DemoFusion as just another node"

[1] Apologies, I'm known for my sarcasm