Add performance comment for get_posts() in Coupon::get_random()

Author: layoutd

includes/Generator/Coupon.php

@@ -151,6 +151,9 @@ public static function batch( $amount, array $args = array() ) {
 	 * @return \WC_Coupon|false Coupon object or false if none available.
 	 */
 	public static function get_random() {
+		// Note: Using posts_per_page=-1 loads all coupons into memory for random selection.
+		// For stores with thousands of coupons, consider using direct SQL with RAND() for better performance.
+		// This approach was chosen for consistency with WordPress APIs and to avoid raw SQL queries.
 		$coupon_ids = get_posts(
 			array(
 				'post_type'      => 'shop_coupon',