While working on #2065
I was reminded that jest does not have adequate TS / ESM support (it still thinks everything is cjs -- and just technically can be set up to work with native ESM, but it's a huuuuge pain, and no one has time for that).

So here is jest replaced by vitest.
I had the option of keeping the "globals" support, but it's better practice to import the things used rather than rely on globals (makes types and eslint easier when imported)

Both before and after this change are 39 test files with 329 tests.