chore(06-02): download and include Action Scheduler library

- Downloaded Action Scheduler 3.9.3 from GitHub
- Placed in vendor/action-scheduler/ directory
- Included in main plugin file before other code for proper initialization
- Library will auto-initialize itself when required

vendor/action-scheduler/classes/ActionScheduler_ActionClaim.php

@@ -0,0 +1,45 @@
+<?php
+
+/**
+ * Class ActionScheduler_ActionClaim
+ */
+class ActionScheduler_ActionClaim {
+	/**
+	 * Claim ID.
+	 *
+	 * @var string
+	 */
+	private $id = '';
+
+	/**
+	 * Claimed action IDs.
+	 *
+	 * @var int[]
+	 */
+	private $action_ids = array();
+
+	/**
+	 * Construct.
+	 *
+	 * @param string $id Claim ID.
+	 * @param int[]  $action_ids Action IDs.
+	 */
+	public function __construct( $id, array $action_ids ) {
+		$this->id         = $id;
+		$this->action_ids = $action_ids;
+	}
+
+	/**
+	 * Get claim ID.
+	 */
+	public function get_id() {
+		return $this->id;
+	}
+
+	/**
+	 * Get IDs of claimed actions.
+	 */
+	public function get_actions() {
+		return $this->action_ids;
+	}
+}