Minimizing Nix Toolbox Gaia CI

[palmskog]

I'm opening this as a memento to adapt Nix Toolbox CI to the new packaging of Gaia. Specifically, the Gaia Hydras package now only depends on the Gaia Schütte part of Gaia, which usually takes less than a minute to check. However, the Nix Toolbox is currently set up to depend on the whole Gaia (albeit with caching). We could probably save a few minutes in fresh CI time.

cc: @Zimmi48

[Zimmi48]

Thanks for the summary. I hadn't followed these changes closely. I'll try to reflect them in nixpkgs and Nix CI later.

[palmskog]

Thanks! Note that the Gaia Schütte package only depends on Dune, Coq, and mathcomp-ssreflect (i.e., mathcomp-algebra is no longer a dependency).