Test running overhaul, switch to Prettier & reformat everything

[defaude]

This PR overhauls the test setup as well as the pipeline

Fixes #1378

Node 20 is now the default minimum engine

This doesn't mean stuff will break if people are using older versions of Node, but they will get a warning during npm install. Vitest should be fine with Node >= 14.18, actually. Nevertheless, it's a reasonable thing to assume everyone has at least the current "active LTS" version of Node available.

Replacing Jest + Babel with Vitest

We already switched to ESM a while ago. There is no need to pump everything through Babel into Jest. Vitest is a blazing-fast drop-in replacement that is mostly Jest-compatible (and definitely better compatible with Jest than Bun is...). This change allows us to drop a ton of npm dependencies.

Remove standard in favor of prettier

There was a .prettierrc file in the repo already, but for some reason we were stuck with standard. I took the liberty to clean up here, as well. It's now prettier only all the way. This means I had to automatically reformat the code once.

Update pipeline

First of all: The long-running test we observed in #1193 is now working just fine when it's running in Vitest on Node 20 🤷

This allows us to run all tests in the pipeline again (and we definitely should). We should also aim for

• only ever merge any PRs when their pipeline is green
• only ever commit & push when the tests are successful (this should be ensured by the pre-commit hook, but I get the feeling that many people are simply suppressing them?)

[appgurueu]

Looks good to me, though I'd prefer keeping line endings at LF in the prettier config unless there is a good reason against it. I also wonder how our CI apparently passed with failing tests (but analyzing or fixing that can be done later, it doesn't have to be in this PR).

Note to self & Rak: Look at the commits individually to not get caught up in the large formatting diff, don't squash.