Optimize Debug Compile Times#33

We previously bumped everything to `opt-level = 3`, which is completely overkill. We really only need `tiny-skia`, which is our renderer, and the `transmute` function, which processes the whole window on every frame, to be fast. While this definitely slows down the performance a little bit overall, the wins in compile times are huge and if you want a fully optimized build, you should be using the release build anyway.