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/deprecated/ActionScheduler_Abstract_QueueRunner_Deprecated.php

@@ -0,0 +1,27 @@
+<?php
+
+/**
+ * Abstract class with common Queue Cleaner functionality.
+ */
+abstract class ActionScheduler_Abstract_QueueRunner_Deprecated {
+
+	/**
+	 * Get the maximum number of seconds a batch can run for.
+	 *
+	 * @deprecated 2.1.1
+	 * @return int The number of seconds.
+	 */
+	protected function get_maximum_execution_time() {
+		_deprecated_function( __METHOD__, '2.1.1', 'ActionScheduler_Abstract_QueueRunner::get_time_limit()' );
+
+		$maximum_execution_time = 30;
+
+		// Apply deprecated filter.
+		if ( has_filter( 'action_scheduler_maximum_execution_time' ) ) {
+			_deprecated_function( 'action_scheduler_maximum_execution_time', '2.1.1', 'action_scheduler_queue_runner_time_limit' );
+			$maximum_execution_time = apply_filters( 'action_scheduler_maximum_execution_time', $maximum_execution_time );
+		}
+
+		return absint( $maximum_execution_time );
+	}
+}