chore(nix): Add rustfmt

flake.nix

@@ -27,7 +27,7 @@
 
         devShell = pkgs.mkShell {
           buildInputs = with pkgs; [openssl];
-          nativeBuildInputs = with pkgs; [rustc cargo rust-analyzer pkg-config clippy];
+          nativeBuildInputs = with pkgs; [rustc cargo rustfmt rust-analyzer pkg-config clippy];
         };
 
         formatter = nixpkgs.legacyPackages.${system}.alejandra;