input: Write a function to create a Python class that takes a given number and calculates the sum of its digits. The class should have an initialization method to store the number and a method to calculate and return the sum of the digits.
  assert SumOfDigits(6342).calculate_sum_of_digits() == 15
  assert SumOfDigits(12345).calculate_sum_of_digits() == 15
  assert SumOfDigits(9876).calculate_sum_of_digits() == 30
  assert SumOfDigits(0).calculate_sum_of_digits() == 0
  assert SumOfDigits(1).calculate_sum_of_digits() == 1
output: class SumOfDigits:
      def __init__(self, number):
          self.number = number
  
      def calculate_sum_of_digits(self):
          return sum(int(digit) for digit in str(self.number))