feat: add typstyle

[leana8959]

Hello,

I have added typstyle, a formatter for typst.

Though, there's a little issue: it's not in the version of nixpkgs pinned by this project, and it won't work. What would be a good solution ?

Thanks and have a nice day :)

[leana8959]

Psst, The CI failed because typstyle is not in the nixpkgs pinned in the flake.

[sandydoo]

I'll bump nixpkgs so that this works out of the box. We'll still need the below changes to ensure it works with older package sets.

[leana8959]

The requested changes were added :)

[sandydoo]

Thanks, @leana8959!