Multi-System with flakes

[blaggacao]

I think it makes sense to preserve this beautiful simplicity:

    (makes.lib.flakes.evaluate { inherit inputs; system = "x86_64-linux"; })

if more system are to be supported, I think makes should follow it's own system namespacing scheme, implemented behind:

    (makes.lib.flakes.evaluate { inherit inputs; systems = supportedSystems; })