feat: add enable options for formatters and checks

cad/default.nix

@@ -96,6 +96,12 @@
               example = "3dfiles";
             };
           };
+
+          formatter = {
+            enable = lib.mkEnableOption "treefmt for formatting multiple types of files" // {default = true;};
+
+            nix = lib.mkEnableOption "formatting for nix files" // {default = true;};
+          };
         };
 
         config = lib.mkIf cfg.enable {
@@ -116,11 +122,6 @@
               // cfg.devShell.extraAttrs;
           };
 
-          # Formatter for nix files, available through 'nix fmt'
-          treefmt = {
-            programs.alejandra.enable = lib.mkDefault true;
-          };
-
           # Your custom packages
           # Accessible through 'nix build', 'nix shell', 'nix run', etc
           packages = lib.mkIf cfg.package.enable {
@@ -152,6 +153,11 @@
                 }
               '';
           };
+
+          # Formatter for nix files, available through 'nix fmt'
+          treefmt = lib.mkIf cfg.formatter.enable {
+            programs.alejandra.enable = lib.mkIf cfg.formatter.nix true;
+          };
         };
       });
     };