fix pkgs -> final in rust overlay, fmt

overlays/rust-toolchain.nix

@@ -1,21 +1,25 @@
 final: prev:
 let
-  mkRustToolchain = toml_path: hash: {
-    fenix-pkgs = (final.fenix.fromToolchainFile {
-      file = toml_path;
-      sha256 = hash;
-    });
-    darwin-pkgs = (with pkgs; lib.optionals stdenv.isDarwin [
-      # Additional darwin specific inputs
-      libiconv
-      darwin.apple_sdk.frameworks.Security
-      darwin.apple_sdk.frameworks.SystemConfiguration
-    ]);
-    complete = [ fenix-pkgs darwin-pkgs ];
-  };
+  mkRustToolchain = toml_path: hash:
+    let
+      fenix-pkgs = (final.fenix.fromToolchainFile {
+        file = toml_path;
+        sha256 = hash;
+      });
+      darwin-pkgs = (with final; lib.optionals stdenv.isDarwin [
+        # Additional darwin specific inputs
+        libiconv
+        darwin.apple_sdk.frameworks.Security
+        darwin.apple_sdk.frameworks.SystemConfiguration
+      ]);
+    in
+    {
+      inherit fenix-pkgs darwin-pkgs;
+      complete = [ fenix-pkgs darwin-pkgs ];
+    };
 in
 {
   lib = prev.lib // {
     inherit mkRustToolchain;
-  }; 
+  };
 }