rework actual-budget to be more generic with test

modules/clan/actual-budget/flake-module.nix

@@ -0,0 +1,19 @@
+{ lib, ... }:
+let
+  module = lib.modules.importApply ./default.nix { };
+in
+{
+  clan.modules = {
+    actual-budget = module;
+  };
+
+  perSystem =
+    { ... }:
+    {
+      clan.nixosTests.actual-budget = {
+        imports = [ ./tests/vm/default.nix ];
+
+        clan.modules."@clan/actual-budget" = module;
+      };
+    };
+}