input: Write a Python function to rotate a 2D array by 90 degrees clockwise.
  assert rotate_90([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]) == [[13, 9, 5, 1], [14, 10, 6, 2], [15, 11, 7, 3], [16, 12, 8, 4]]
  assert rotate_90([[1, 2], [3, 4]]) == [[3, 1], [4, 2]]
  assert rotate_90([[1]]) == [[1]]
output: def rotate_90(matrix):
      return [list(row) for row in zip(*matrix[::-1])]