Add the nix flake for the cyberpunk splash screen

flake.nix

@@ -78,6 +78,11 @@
               rootFeatures = [ "screenplay" ];
               release = true;
             }).rootCrate.build;
+            cyberpunk-splash = (import ./cyberpunk-splash/Cargo.nix {
+              inherit pkgs;
+              buildRustCrateForPkgs = customBuildInfo;
+              release = true;
+            }).rootCrate.build;
           };
     };
 }