input: Write a python function to normalize a 2D numpy array and assert that the maximum value of each element is 1.
  assert np.amax(normalize_array(np.array([[1, 2, 3], [4, 5, 6]]))) == 1.0
  assert np.amax(normalize_array(np.array([[10, 20, 30], [40, 50, 60]]))) == 1.0
  assert np.amax(normalize_array(np.array([[100, 200, 300], [400, 500, 600]]))) == 1.0
output: import numpy as np
  
  def normalize_array(arr):
      max_val = np.amax(arr)
      return arr / max_val