input: Write a python function to generate a random number between a given range using a class.
  assert 10 <= RandNumGenerator(10, 50).generate_rand_num() <= 50
  assert 0 <= RandNumGenerator(0, 100).generate_rand_num() <= 100
  assert -10 <= RandNumGenerator(-10, 10).generate_rand_num() <= 10
output: import random
  
  class RandNumGenerator:
      def __init__(self, start, end):
          self.start = start
          self.end = end
  
      def generate_rand_num(self):
          return random.randint(self.start, self.end)