Karma needs a replacement

[jonkoops]

We're still relying on Karma, which has been deprecated. An alternative will be required going forward. Since our test suite will have to support both browsers and Node.js, the choices are limited to Jasmine and Vitest, as Web Test Runner only supports browsers, and Jest only supports Node.js.

I already have the current test suite running with Jasmine, which was not too much of an effort in terms of modifications. It does however seem to be constantly declining in popularity (now at ~1.5 million downloads a week), and is less actively maintained, whereas Vitest is growing in popularity (~3.8 million downloads a week) with a lot of activity on the repository.

@puleos @addaleax considering these choices, which action do you believe we should be taking here? Note that both of these options will force us to raise the Node.js versions we run the tests on.