feat: improve flake structure

modules/flakeDefaults.nix

@@ -0,0 +1,17 @@
+{ pkgs, lib, self, inputs, ... }:
+
+let
+  flakes = lib.filterAttrs (name: value: value ? outputs) inputs;
+  nixRegistry = builtins.mapAttrs (name: v: { flake = v; }) flakes;
+in {
+  # Let 'nixos-version --json' know about the Git revision
+  # of this flake.
+  system.configurationRevision = lib.mkIf (self ? rev) self.rev;
+
+  nix = {
+    extraOptions = "experimental-features = nix-command flakes";
+    nixPath = lib.mapAttrsToList (n: v: "${n}=${v}") flakes;
+    registry = nixRegistry;
+    package = pkgs.nixUnstable;
+  };
+}