fix(ns): root-qualify WP_* classes after PSR-4 move

Bare WP_REST_Server etc. resolve under AKSRT\* namespaces; prefix with
\ for Balance REST and other type hints / constructors.

src/AKSRT/Credits/Credits.php

@@ -263,7 +263,7 @@ class Credits {
             $q['search'] = '*' . esc_attr((string) $args['search']) . '*';
             $q['search_columns'] = ['user_login', 'user_email', 'display_name', 'user_nicename'];
         }
-        $user_query = new WP_User_Query($q);
+        $user_query = new \WP_User_Query($q);
         $users = $user_query->get_results();
         $items = [];
         foreach ($users as $u) {