Add EmptyResponse class for void endpoints

src/Data/Responses/EmptyResponse.php

···
+<?php
+
+namespace SocialDept\AtpClient\Data\Responses;
+
+use Illuminate\Contracts\Support\Arrayable;
+
+/**
+ * Response class for endpoints that return empty objects.
+ *
+ * @implements Arrayable<string, mixed>
+ */
+class EmptyResponse implements Arrayable
+{
+    public function __construct() {}
+
+    public static function fromArray(array $data): self
+    {
+        return new self;
+    }
+
+    public function toArray(): array
+    {
+        return [];
+    }
+}