Add nix-fast-build

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

flake.nix

@@ -189,7 +189,28 @@
         devShells.${system} = import ./hosts/common/shells { inherit pkgs; };
         packages.${system} = import ./packages { inherit pkgs; };
         formatter.${system} = treefmt.config.build.wrapper;
-        checks.${system}.formatting = treefmt.config.build.check inputs.self;
+
+        checks.${system} =
+          let
+            nixosConfigurations =
+              pkgs.lib.mapAttrs'
+                (
+                  name: config:
+                  pkgs.lib.nameValuePair "nixosConfiguration-${name}" config.config.system.build.toplevel
+                )
+                ((pkgs.lib.filterAttrs (_: config: config.pkgs.system == system)) inputs.self.nixosConfigurations);
+
+            packages = pkgs.lib.mapAttrs' (n: pkgs.lib.nameValuePair "package-${n}") inputs.self.packages;
+
+            overlayPackages = pkgs.lib.mapAttrs' (n: pkgs.lib.nameValuePair "overlayPackage-${n}") (
+              import ./overlays/packages.nix { inherit pkgs; }
+            );
+
+            devShells = pkgs.lib.mapAttrs' (n: pkgs.lib.nameValuePair "devShell-${n}") inputs.self.devShells;
+
+            formatter.formatting = treefmt.config.build.check inputs.self;
+          in
+          nixosConfigurations // packages // overlayPackages // devShells // formatter;
       }
     );
 }