Clean up the API for ComfyUI initialization through code (currently happens automatically through importation)

Hi, I use ComfyUI directly in my codebase for AI animation and currently the whole ComfyUI initialization process is a little hard to schedule, as it is tied to code running at top level directly when importing some of the stuff. I'm not deep into Python but I think in general that kind of architecture is a little dubious, would be better off stuffing things into a function we can invoke right when we mean to initialize the core.