flake.nix: refactoring using flake-parts

flake-modules/overlays.nix

@@ -0,0 +1,21 @@
+{inputs, ...}: {
+  imports = [
+    inputs.flake-parts.flakeModules.easyOverlay
+  ];
+  perSystem = {
+    config,
+    pkgs,
+    final,
+    ...
+  }: {
+    overlayAttrs = {
+      nixvim = {
+        inherit
+          (config.legacyPackages)
+          makeNixvim
+          makeNixvimWithModule
+          ;
+      };
+    };
+  };
+}