Two versions of nixpkgs pulled

[GrigorenkoPV]

This flake depends on two versions of nixpkgs: nixpkgs-unstable & nixos-23.05.

From what I can tell, it uses unstable as a fallback for stable.

However, this means that both versions get pulled when using this in another flake (unless you override both nixpkgs & nixpkgs-stable to follow the same version).

I recently had to spend some time on a slow cellular connection, where it would take 2.5 minutes to pull 1 version of nixpkgs. 2 version would thus take 5 minutes, which is a noticeable slowdown.

So the question is, can we get rid of one of the versions?