duration method
Travel time from the current position to the end of the route.
Implementation
Duration? duration() {
  final routePosition = this.routePosition;
  final endPosition = route.route.geometry.last?.point;
  if (routePosition == null || endPosition == null) {
    return null;
  }
  final duration = dynamicRouteInfo.traffic.durations
      .calculateDuration(routePosition, endPosition);
  return duration;
}