chore(devshell): add vault package to development shell

- Added the `vault` package to the list of dev shell packages.
- Adjusted formatting for parameter list to align with style conventions.

nix/devshell.nix

@@ -1,7 +1,7 @@
-{
-  pkgs,
-  vault-hier,
-  rustVersion,
+{ pkgs
+, vault-hier
+, rustVersion
+,
 }:
 
 let
@@ -19,6 +19,7 @@ pkgs.mkShell {
   packages = with pkgs; [
     vault-hier # Add the vault-hier package to the dev shell
     toolchain_with_src # Add the custom Rust toolchain with source code to the dev shell
+    vault
   ];
   nativeBuildInputs = [
     vault-hier