Switch package manager to `pnpm` or `npm`

[flevi29]

A lot of high profile repositories these days use pnpm, for instance:

• https://github.com/sveltejs/svelte
• https://github.com/vitejs/vite
• https://github.com/vuejs/core

I was looking into upgrading Yarn, but it looks like to make full use of the latest Yarn, we'd have to make some trade-offs and non-standard changes.

• they don't have a standard way to use Yarn with GitHub actions
• to make full use of the latest version we'd have to use their "Plug'n'Play" feature, which diverges way too much from how Node.js has always handled dependencies (and ESM support is still (in Anum Domini 2025) experimental this way)
  • and most importantly every IDE needs an additional extension and additional setup to work with it

Instead I will be switching to pnpm, and I will do so for every JS/TS repository in the meilisearch org, if you'll allow me.