feat: refactor flake.nix

systems/darwin.nix

@@ -0,0 +1,17 @@
+args:
+with args; let
+  macosSystem = import ../lib/macosSystem.nix;
+  system = x64_darwin;
+  base_args = {
+    inherit nix-darwin home-manager system;
+    specialArgs = x64_darwin_specialArgs;
+    nixpkgs = nixpkgs-darwin;
+  };
+in {
+  # macOS's configuration, for work.
+  darwinConfigurations = {
+    harmonica =
+      macosSystem (base_args
+        // darwin_harmonica_modules);
+  };
+}