feat(home): Add substituters & other nix niceties

modules/home/base/nix/default.nix

@@ -4,16 +4,34 @@
     nix = {
       package = pkgs.lix;
 
+      settings = {
+        trusted-users = [
+          "root"
+          config.marleyos.my.name
+        ];
+
         # Enable flakes.
-      settings.experimental-features = [
+        experimental-features = [
           "nix-command"
           "flakes"
         ];
 
+        # Set up caches.
+        extra-substituters = [
+          "https://marleyos.cachix.org"
+          "https://nix-community.cachix.org"
+        ];
+
+        trusted-public-keys = [
+          "marleyos.cachix.org-1:q2kEtqvS5CoQ8BmKlWOfOnN+fi4gUoSuL6HRKy37eCA="
+          "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+        ];
+
         # Disable that annoying "git tree is dirty" warning.
-      extraOptions = ''
-        warn-dirty = false
-      '';
+        warn-dirty = false;
+
+        auto-optimise-store = true;
+      };
 
       # Garbage collection.
       gc.automatic = true;