feat: Working encrypt and decrypt commands.

Sources/hpa/VaultCommands/DecryptCommand.swift

@@ -18,6 +18,14 @@ struct DecryptCommand: AsyncParsableCommand {
   var output: String?
 
   mutating func run() async throws {
-    fatalError()
+    var args = ["decrypt"]
+    if let output {
+      args.append(contentsOf: ["--output", output])
+    }
+    try await runVault(
+      commandName: Self.commandName,
+      options: options,
+      args
+    )
   }
 }