input: Write a python function to create a 2D numpy array filled with ones, given the number of rows and columns.
  assert np.array_equal(create_ones_array(2, 3), np.ones((2, 3)))
  assert np.array_equal(create_ones_array(4, 5), np.ones((4, 5)))
  assert np.array_equal(create_ones_array(1, 1), np.ones((1, 1)))
output: import numpy as np
  
  def create_ones_array(rows, cols):
      return np.ones((rows, cols))