replace mocha with vitest

[felixroos]

• refactored all the tests to vitest syntax
• tune test not yet refactored
• blocked by cannot assign imported module to globalThis vitest-dev/vitest#1807

[felixroos]

fixes #145

[felixroos]

waiting for vitest@0.21.1 https://www.npmjs.com/package/vitest

[felixroos]

i have now refactored all tests to vitest + now using the snapshot feature instead of the custom solution. unfortunately, it's actually slower than mocha by ~50% so I am a bit disappointed.. it seems vitest has had a performance drop lately, so hopefully this will get better soon

[felixroos]

i think it's still better, because the dev mode seems much quicker + the snapshot feature alone will be of great use. also, if we decide to move to typescript later, this will automatically work. I'll merge this