input: Write a python function to calculate the mean squared error (MSE) between two lists of equal length.
  assert mse_loss([1, 2, 3, 4, 5], [2, 3, 4, 5, 6]) == 1.2
  assert mse_loss([0, 0, 0, 0, 0], [1, 1, 1, 1, 1]) == 1.0
  assert mse_loss([10, 20, 30, 40, 50], [15, 25, 35, 45, 55]) == 25.0
output: def mse_loss(y_true, y_pred):
      return sum((yt - yp) ** 2 for yt, yp in zip(y_true, y_pred)) / len(y_true)