the plugin lacks the completion class required by moodle 4 for custom completions

[attilioariadne1985]

when a reservation mod instance is modified the activity is automatically completed for all students in the course.
This happens because the required object class in the lib/completionlib.php file is missing from the internal_get_state function.

The snippet of code in question is the following:

$cmcompletionclass = activity_custom_completion::get_cm_completion_class($cminfo->modname);
if ($cmcompletionclass) {
/** @var activity_custom_completion $cmcompletion */
$cmcompletion = new $cmcompletionclass($cminfo, $userid, $completionstate);
$response = $cmcompletion->get_overall_completion_state() != COMPLETION_INCOMPLETE;
}

The missing class must contain methods including get_overall_completion_state() which replaces the old reservation_get_completion_state method which is now in the plugin lib