buildClan function: export all machines via nixosModules/darwinModules

We want each machine not only to be exposed via nixosConfigurations but also as a module.
This allows re-importing the machine in tests and override the architecture for example.

lib/build-clan/public.nix

@@ -14,6 +14,8 @@
   topLevel = [
     "clanInternals"
     "nixosConfigurations"
+    "nixosModules"
     "darwinConfigurations"
+    "darwinModules"
   ];
 }