input: Write a python function to calculate the mean absolute error between two lists using numpy.
  assert mean_absolute_error(np.array([1, 2, 3]), np.array([1, 2, 3])) == 0.0
  assert mean_absolute_error(np.array([1, 2, 3]), np.array([4, 5, 6])) == 3.0
  assert mean_absolute_error(np.array([10, 20, 30]), np.array([5, 25, 35])) == 10.0
output: import numpy as np
  
  def mean_absolute_error(y_true, y_pred):
      return np.mean(np.abs(y_true - y_pred))