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/migration/BatchFetcher.php

@@ -0,0 +1,95 @@
+<?php
+
+namespace Action_Scheduler\Migration;
+
+use ActionScheduler_Store as Store;
+
+/**
+ * Class BatchFetcher
+ *
+ * @package Action_Scheduler\Migration
+ *
+ * @since 3.0.0
+ *
+ * @codeCoverageIgnore
+ */
+class BatchFetcher {
+	/**
+	 * Store instance.
+	 *
+	 * @var ActionScheduler_Store
+	 */
+	private $store;
+
+	/**
+	 * BatchFetcher constructor.
+	 *
+	 * @param ActionScheduler_Store $source_store Source store object.
+	 */
+	public function __construct( Store $source_store ) {
+		$this->store = $source_store;
+	}
+
+	/**
+	 * Retrieve a list of actions.
+	 *
+	 * @param int $count The number of actions to retrieve.
+	 *
+	 * @return int[] A list of action IDs
+	 */
+	public function fetch( $count = 10 ) {
+		foreach ( $this->get_query_strategies( $count ) as $query ) {
+			$action_ids = $this->store->query_actions( $query );
+			if ( ! empty( $action_ids ) ) {
+				return $action_ids;
+			}
+		}
+
+		return array();
+	}
+
+	/**
+	 * Generate a list of prioritized of action search parameters.
+	 *
+	 * @param int $count Number of actions to find.
+	 *
+	 * @return array
+	 */
+	private function get_query_strategies( $count ) {
+		$now  = as_get_datetime_object();
+		$args = array(
+			'date'     => $now,
+			'per_page' => $count,
+			'offset'   => 0,
+			'orderby'  => 'date',
+			'order'    => 'ASC',
+		);
+
+		$priorities = array(
+			Store::STATUS_PENDING,
+			Store::STATUS_FAILED,
+			Store::STATUS_CANCELED,
+			Store::STATUS_COMPLETE,
+			Store::STATUS_RUNNING,
+			'', // any other unanticipated status.
+		);
+
+		foreach ( $priorities as $status ) {
+			yield wp_parse_args(
+				array(
+					'status'       => $status,
+					'date_compare' => '<=',
+				),
+				$args
+			);
+
+			yield wp_parse_args(
+				array(
+					'status'       => $status,
+					'date_compare' => '>=',
+				),
+				$args
+			);
+		}
+	}
+}