input: Write a python function to return the squares of an array in Python.
  assert square_array([1, 2, 3, 4, 5]) == [1, 4, 9, 16, 25]
  assert square_array([0, -1, -2, -3]) == [0, 1, 4, 9]
  assert square_array([2, 4, 6, 8]) == [4, 16, 36, 64]
output: def square_array(arr):
      return [x ** 2 for x in arr]