Tests not working anymore after Node > 18

[Fuzzyma]

Installing this repository has some challenges.
The engine field is set to Node >12. However, Node 12 cant be used because some dependencies at least require Node 14.
In Node 20 the tests start failing because mockFS is not mocking the file system anymore.

So we probably want to set the engine field to Node version 14.21.3 til 18.18.2. I didnt test node 19 since it wasnt LTS but it breaks in Node 20.

I also had problems with yarn versin 3 so I had to install yarn v1 (which by itself is a challenge if corepack is enabled).

So here is what I used in the end:

nvm use 18
npm i yarn # not globally because it conflicts with corepack and corepack will use yarn 3
rm package-lock.json
npx yarn
npx yarn build
npx yarn test

Just leaving this here for others to notice. I am not sure if this package is still relevant for newer node versions but in that case we probably wanna modernice all dependencies