fix: treefmt on nixos-unstable

[dantefromhell]

nixpkgs@dcb250a introduced some changes to the treefmt package:

• the treefmt package is treefmt v2 aka the go version)
• the treefmt1 package throws an eval error

resulting in broken std devens as they trigger the eval error for treefmt1.

std@febf2ee explicitly selects the discontinued rust implementation due to unfixed bugs in 24.11 for treefmt < 2.1.1.

The std repo still uses the 23.11 nixpkgs release.

@blaggacao I'm not sure what the best path forward is for this change to not break backwards compatibility, please advise.

Until this is sorted I'll leave this PR as draft for further discussion.

[blaggacao]

Is there any need to switch to the new packages, while the old is still in nixpkgs? My reasoning is that once the new is a full and equal replacement, the old one will be removed and this code will just continue to wirk fine.

[korrat]

With current nixpkgs-unstable, the lines in question evaluate to an error pointing out the removal of treefmt1.

This is especially problematic for the treefmt configuration preset because it cannot be overriden easily.

[blaggacao]

Ok, then let's switch to nixpkgs.treefmt, in that case, an hope the treefmt rewrite is stable and bug-free, now.

[oneingan]

plan to merge this?

[dantefromhell]

Apologies for the delay and thanks @blaggacao for making the call.

I've marked the PR as ready to review.

[blaggacao]

Let's go, then! Thanks a lot!