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/abstracts/ActionScheduler_WPCLI_Command.php

@@ -0,0 +1,83 @@
+<?php
+
+/**
+ * Abstract for WP-CLI commands.
+ */
+abstract class ActionScheduler_WPCLI_Command extends \WP_CLI_Command {
+
+	const DATE_FORMAT = 'Y-m-d H:i:s O';
+
+	/**
+	 * Keyed arguments.
+	 *
+	 * @var string[]
+	 */
+	protected $args;
+
+	/**
+	 * Positional arguments.
+	 *
+	 * @var array<string, string>
+	 */
+	protected $assoc_args;
+
+	/**
+	 * Construct.
+	 *
+	 * @param string[]              $args       Positional arguments.
+	 * @param array<string, string> $assoc_args Keyed arguments.
+	 * @throws \Exception When loading a CLI command file outside of WP CLI context.
+	 */
+	public function __construct( array $args, array $assoc_args ) {
+		if ( ! defined( 'WP_CLI' ) || ! constant( 'WP_CLI' ) ) {
+			/* translators: %s php class name */
+			throw new \Exception( sprintf( __( 'The %s class can only be run within WP CLI.', 'action-scheduler' ), get_class( $this ) ) );
+		}
+
+		$this->args       = $args;
+		$this->assoc_args = $assoc_args;
+	}
+
+	/**
+	 * Execute command.
+	 */
+	abstract public function execute();
+
+	/**
+	 * Get the scheduled date in a human friendly format.
+	 *
+	 * @see ActionScheduler_ListTable::get_schedule_display_string()
+	 * @param ActionScheduler_Schedule $schedule Schedule.
+	 * @return string
+	 */
+	protected function get_schedule_display_string( ActionScheduler_Schedule $schedule ) {
+
+		$schedule_display_string = '';
+
+		if ( ! $schedule->get_date() ) {
+			return '0000-00-00 00:00:00';
+		}
+
+		$next_timestamp = $schedule->get_date()->getTimestamp();
+
+		$schedule_display_string .= $schedule->get_date()->format( static::DATE_FORMAT );
+
+		return $schedule_display_string;
+	}
+
+	/**
+	 * Transforms arguments with '__' from CSV into expected arrays.
+	 *
+	 * @see \WP_CLI\CommandWithDBObject::process_csv_arguments_to_arrays()
+	 * @link https://github.com/wp-cli/entity-command/blob/c270cc9a2367cb8f5845f26a6b5e203397c91392/src/WP_CLI/CommandWithDBObject.php#L99
+	 * @return void
+	 */
+	protected function process_csv_arguments_to_arrays() {
+		foreach ( $this->assoc_args as $k => $v ) {
+			if ( false !== strpos( $k, '__' ) ) {
+				$this->assoc_args[ $k ] = explode( ',', $v );
+			}
+		}
+	}
+
+}