chore: clear babel cache on a weekly basis

[merceyz]

What's the problem this PR addresses?

Given enough time the Babel cache will grow enough to slow down running Yarn in this repo by quite a lot. In my case the cache has been growing since 19.02.2021 and is now at 422MB taking ~6 seconds to save.

How did you fix it?

• Add the current week since the UNIX epoch to the babel cache key
• Updated @babel/register for babel-register: Don’t rewrite the cache if it’s not dirty babel/babel#12813 so the cache is only written when it changes saving an additional ~400ms

Result

$ time yarn --version
3.0.0-rc.2.dev

________________________________________________________
- Executed in   14.14 secs      fish           external
+ Executed in    2.62 secs      fish           external

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.