[Feature Request]: Image preload range when using AI tools

### Preflight Checklist - [x] I have searched the [issue tracker](https://www.github.com/ollm/OpenComic/issues) for a feature request that matches the one I want to file, without success. ### Describe your suggested feature For the upcoming AI models specifically for OpenComic, I'd like to suggest a slider in common settings or under AI tools configuration. This option lets GPU process the next few pages ahead while you're on the current page, so that you can keep reading without having to wait for the next page to be fully processed. Since running AI takes time, this will help users with mid to low end PCs improve reading experience by reducing wait time. I think the slider ranging from `2` to `10` pages should suffice for now, but more AI tools being active means we may need to preload more pages.