feat: upgrade Node.js and related nix files

[o-az]

Summary:

• upgrade Node.js to v21,
• upgrade svelte-language-server and typescript-language-server to latest.
  @PoisonPhang suggested following our current approach when we need to use the latest version of a tool: this Node.js upgrade follows our current approach by supplying a separate nixpkgs, the same way we nixify solc and go:
  

  union/flake.nix

  Line 12 in dfbd745

  nixpkgs-nodejs.url = "github:NixOS/nixpkgs/nixos-unstable";

Why upgrade:

• Need up to date svelte-language-server and typescript-language-server as they were quite behind in terms of what versions of svelte and typescript they covered,
• v21 fixes a couple of bugs, upgrades npm to v10,
• To overcome the recurring node-gyp issue. It hasn't been possible to update Astro since every version post-4.0.9 resulted in that nasty sharp x node-gyp issue. To overcome that issue, I tested a scenario that worked: building the site with Node.js v21 and overriding sharp version. To override sharp's version, simply adding sharp to package.json doesn't work because other dependencies also have sharp as their dependency with different versions:

   npm ls sharp
   
   ├─┬ [email protected]
   │ └── [email protected] # different version
   └── [email protected] # version in package.json

  Long story short, I upgraded Node.js to v21 and leveraged npm's overrides field which lets me override the version of any dependency down the tree. So now:

   npm ls sharp
   
   ├─┬ [email protected]
   │ └── [email protected] overridden
   └── [email protected] overridden

[github-actions]

Site/Docs 🤠

✨ Deployment complete! Take a peek over at https://9b10d23d.docs-19u.pages.dev

2024-02-07T02:02:52Z

[github-actions]

App 🤌

✨ Deployment complete! Take a peek over at https://ce43b309.app-1b1.pages.dev

2024-02-07T02:02:52Z

[cor]

Great PR! node projects are the most difficult to package/manage in Nix for sure bc of the node-gyp stuff, and you managed to find a way for us to be on the latest versions of dependencies without issues with sharp. Great job sir