clan-nixos-test: pass clan-core to test nodes via module args

This allows tests that need access to clan-core (e.g. for clan-cli or
dependencies) to use it within their node configurations.

lib/flake-parts/clan-nixos-test.nix

@@ -45,6 +45,14 @@ in
                       ];
 
                       hostPkgs = pkgs;
+
+                      defaults = {
+                        imports = [
+                          {
+                            _module.args.clan-core = self;
+                          }
+                        ];
+                      };
                     }
                   );
                 in
@@ -65,6 +73,14 @@ in
                   ];
 
                   hostPkgs = pkgs;
+
+                  defaults = {
+                    imports = [
+                      {
+                        _module.args.clan-core = self;
+                      }
+                    ];
+                  };
                 }
               )
             ) cfg)