feat(tests): add eval tests for darwin systems

outputs/aarch64-darwin/tests/hostname/expected.nix

@@ -0,0 +1,8 @@
+{
+  lib,
+  outputs,
+}: let
+  hostsNames = builtins.attrNames outputs.darwinConfigurations;
+  expected = lib.genAttrs hostsNames (name: name);
+in
+  expected

outputs/aarch64-darwin/tests/hostname/expr.nix

@@ -0,0 +1,9 @@
+{
+  lib,
+  outputs,
+}:
+lib.genAttrs
+(builtins.attrNames outputs.darwinConfigurations)
+(
+  name: outputs.darwinConfigurations.${name}.config.networking.hostName
+)