input: Write a python function to normalize a list of numbers using numpy.
  assert np.allclose(normalize([1, 2, 3, 4]), [-1.34164079, -0.4472136, 0.4472136, 1.34164079])
  assert np.allclose(normalize([10, 20, 30, 40, 50]), [-1.41421356, -0.70710678, 0., 0.70710678, 1.41421356])
  assert np.allclose(normalize([5, 15, 25]), [-1.22474487, 0., 1.22474487])
output: import numpy as np
  
  def normalize(numbers):
      mean = np.mean(numbers)
      std_dev = np.std(numbers)
      return (numbers - mean) / std_dev