Finally solved the problems with the imgui renderer after a long chat with clankers. Fixed some other stuff as well.
Reminder to keep the rendered_this_frame check as that's what solved it. Probably a deeper issue down there that caused us to render twice, but whatever.
- Move engine to a different crate
- Add engine trait
- Refactor the rest of the codebase to work with these changes
- Add debug ui buffer, use it to finish imgui support
