[Request] Add channels

[takuyahara]

The selectable channel is either nixos' stable or unstable one, so that (as of now) nixos-25.05 or nixos-unstable. Nix Channel Status seems defining major channels and I want them, particulary nixpkgs-unstable to be covered, so it would be great if channel can be selected from the followings.

• nixpkgs-unstable
• nixos-unstable-small
• nixos-unstable
• nixpkgs-25.05-darwin
• nixos-25.05-small
• nixos-25.05

[raboof]

This would considerably grow the import jobs and index size. Since your system will not necessarily be 'exactly' in sync with any channel anyway, it's hard to say how valuable this would be. Let's collect more feedback in this issue first.