refactor: migrate to vitest

[antfu]

Thanks a lot to @JessicaSachs 🙌

[JessicaSachs]

So I was getting an issue before I upgraded to 0.0.108 where those tests would fail. (the "tests magically work now" commit).

I think the upgrade to 0.0.108 made vitest fast enough that the race condition isn't apparent on my machine, but it still fails in CI (slower CPU, etc). All of the tests that are broken mock or other-wise reset window/DOM state. e.g. document.location, window.localStorage, window.navigator, document.body

To reproduce the failure, you must run all tests together. Most of the time I spent was trying to debug why those tests were failing. I couldn't figure it out. I think, environmentally, this environment isn't as pure/sandboxed as jest's jsdom resets.