feat: add nix flake and .devcontainer.json

[lajp]

Description

• add nix flake and .devcontainer.json to make setting up the development environment trivial

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Formatting and linting

• Format code with pnpm format and lint the project with pnpm lint

[MikaelSiidorow]

Didn't quite work first try, but restarting VSCode twice it seems to now work. No config needed.

First try failed during initializing devcontainer, but automatically prompted to retry
Second try it didn't find node or pnpm and couldn't start the dev server, didn't prompt a restart and I did it manually
Third try pnpm dev worked fine and everything seems to work

Nix Node version is a bit behind what we have in pkg.json and it gives a warning, but doesn't seem to break anything.

Should we also add some of the tasks to VSCode config? For dev, lint etc 🤔 Though it might be a good idea to still force using the terminal for learning

[MikaelSiidorow]

There also seems to be some trouble loading the tsserver from the workspace. It doesn't have typescript in node_modules 👀

The second problem not finding node or pnpm seems to be a sort of race condition, second time I rebuilt the devcontainer it worked simply after waiting a few seconds

[lajp]

Tasks could be a good idea, I also considered using devenv processes to start the db and pnpm dev automatically, but I think it is in our interest to keep the instructions for developing with and without a dev container the same.

[MikaelSiidorow]

There's a race condition with the ESLint extension and loading Node.js in the devcontainer atm. Node doesn't exist when eslint extension is trying to access it, and it doesn't seem to work even with restarts

[lajp]

There's a race condition with the ESLint extension and loading Node.js in the devcontainer atm. Node doesn't exist when eslint extension is trying to access it, and it doesn't seem to work even with restarts

This is something that should be handled by the direnv extension. I'll look into it at some point.