Migrate from yarn 1.x to 4.x

[xyloflake]

Why do it?

1. Yarn 4.x has lot of optimizations that yarn classic doesn't. This saves dev time.
2. Yarn 4.x allows custom patching of dependencies, which is a super important feature we'd want.
3. Yarn 1.x feels old, outdated and slow
4. Stability
5. See benefits

How to update yarn version?

As per official docs, assuming that you're in muffon's root src directory,

corepack enable
yarn set version berry
yarn install
yarn