Migrate to vitest

This MR migrates the tests to vitest.

I think this migration is benifitial for us because of the following reasons:

• vitest is faster than jest
• vitest has typescript support out of the box (should resolve issues with weird code coverage)
• the GEMIMEG-Tool will use vite aswell at some point in the future (because of Vue 3 and Nuxt)

See https://vitest.dev/guide/comparisons.html