input: Write a python function to compute the histogram of color channels of an image and concatenate them into a single feature vector.
  assert np.array_equal(color_hist(np.array([[[0, 0, 0], [255, 255, 255]], [[128, 128, 128], [64, 64, 64]]])), np.concatenate((np.histogram([0, 255, 128, 64], bins=32)[0], np.histogram([0, 255, 128, 64], bins=32)[0], np.histogram([0, 255, 128, 64], bins=32)[0])))
  assert len(color_hist(np.random.randint(0, 256, (100, 100, 3)), 32)) == 96
  assert len(color_hist(np.random.randint(0, 256, (50, 50, 3)), 16)) == 48
output: import numpy as np
  
  def color_hist(image, bins=32):
      hist_r = np.histogram(image[:, :, 0], bins=bins, range=(0, 256))[0]
      hist_g = np.histogram(image[:, :, 1], bins=bins, range=(0, 256))[0]
      hist_b = np.histogram(image[:, :, 2], bins=bins, range=(0, 256))[0]
      return np.concatenate((hist_r, hist_g, hist_b))