input: Write a function to generate a random hexadecimal string of a specified length.
  assert len(generate_random_hex_string(24)) == 48
  assert len(generate_random_hex_string(16)) == 32
  assert len(generate_random_hex_string(8)) == 16
output: import random
  
  def generate_random_hex_string(length):
      return ''.join(random.choices('0123456789abcdef', k=length*2))