[tests] migrate from jest to vitest (#3940)

This is a big change, but I think it's a good move, as `vitest` is much
more modern than `jest`.

I'm excited about the UI watch feature (run `npm run test:ui`), for
example - it's really helpful and saves time when debugging tests. I had
to adjust a few tests because they had time related issues, but
basically we are now testing the same things - even a bit better and
less flaky (I hope).

What do you think?

js/module_functions.js

@@ -5,8 +5,8 @@
  * @param {Promise} callback function to call when the timer expires
  */
 const scheduleTimer = function (timer, intervalMS, callback) {
-	if (process.env.JEST_WORKER_ID === undefined) {
-		// only set timer when not running in jest
+	if (process.env.mmTestMode !== "true") {
+		// only set timer when not running in test mode
 		let tmr = timer;
 		clearTimeout(tmr);
 		tmr = setTimeout(function () {