fix fuzz setup

fuzz/flake.nix

@@ -0,0 +1,22 @@
+{
+  inputs = {
+    utils.url = "github:numtide/flake-utils";
+    nixpkgs.url = "nixpkgs/release-22.11";
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    utils,
+  }:
+    utils.lib.eachDefaultSystem (system: let
+      pkgs = (import nixpkgs) {
+        inherit system;
+      };
+    in rec {
+      # `nix develop`
+      devShell = pkgs.mkShell {
+        nativeBuildInputs = with pkgs; [rustup cargo-edit cargo-fuzz];
+      };
+    });
+}