refactor: init hello-world module with unit tests (eval)

clanServices/hello-world/flake-module.nix

@@ -0,0 +1,37 @@
+{
+  self,
+  inputs,
+  lib,
+  ...
+}:
+let
+  module = lib.modules.importApply ./default.nix {
+    inherit (self) packages;
+  };
+in
+{
+  clan.inventory.modules = {
+    hello-world = module;
+  };
+  perSystem =
+    { ... }:
+    let
+      # Module that contains the tests
+      # This module adds:
+      # - legacyPackages.<system>.eval-tests-hello-world
+      # - checks.<system>.eval-tests-hello-world
+      unit-test-module = (
+        self.clanLib.test.flakeModules.makeEvalChecks {
+          inherit module;
+          inherit self inputs;
+          testName = "hello-world";
+          tests = ./tests/eval-tests.nix;
+          # Optional arguments passed to the test
+          testArgs = { };
+        }
+      );
+    in
+    {
+      imports = [ unit-test-module ];
+    };
+}