docs: def average_build_duration(connection, package):
      """
      Return the average build duration for a package (or container).
  
      :param connection: txkoji.Connection
      :param package: package name
      :returns: deferred that when fired returns a datetime.timedelta object
      """
      if isinstance(package, str) and package.endswith('-container'):
          return average_last_builds(connection, package)
      return connection.getAverageBuildDuration(package)