category hierarchy level as a body class – parent cat =1, child cat=2, grandchild=3

You can achieve this by using the following custom code. You can use the code by adding it in the functions.php file of child theme or in the custom plugin file.

add_filter( 'body_class', 'custom_cat_archiev_class' );
function custom_cat_archiev_class( $classes ) {
    if ( is_category() ) {
        $cat = get_queried_object();
        $ancestors = get_ancestors( $cat->term_id, 'category', 'taxonomy' );
        $classes[] = 'catlevel-' . ( count( $ancestors ) + 1 );
    }
    return $classes;
}