Improve development in NixOS

[krishnans2006]

Improves upon #93 (but does not solve it yet).

This PR allows ruff to be installed and run from the Nix store (instead of as a pip package), making it work. However, ruff will still not work within pre-commit.

[JasonGrace2282]

When I try it, I end up with an older version of ruff for some reason. Is this just a me problem?

docker exec -it nixos/nix
git clone https://github.com/tjcsl/tin
cd tin
git fetch origin pull/94/head:nix-ruff
git switch nix-ruff
nix develop --extra-experimental-features nix-command --extra-experimental-features flakes
ruff --version

Gives a ruff version of 0.4.4, two major versions behind what's used in CI.

[krishnans2006]

When I try it, I end up with an older version of ruff for some reason. Is this just a me problem?

Nope, happens for me too. It's quite annoying how Nixpkgs does versioning...

One solution here is to use Nixpkgs unstable, but that still requires constant lockfile bumps whenever we upgrade ruff on pre-commit. I'll look into it and see if there's something better.

[JasonGrace2282]

We can always just have nixpkgs unstable as another flake input, although I'm not quite sure how to pin the ruff version without pinning to a nixpkgs commit hash.

[krishnans2006]

Yeah, and even if we are able to pin a ruff version, I think it would be way too annoying to bump it every time we merge in a pre-commit autoupdate (like #89).

Maybe the best solution is just to use the most recent ruff always, but is that even possible? (add flake.lock to gitignore?)