input: Write a python function to calculate the sum of squares of all integers between two given numbers n and m (inclusive).
  assert sum_of_squares(1, 3) == 14
  assert sum_of_squares(4, 4) == 16
  assert sum_of_squares(1, 5) == 55
output: def sum_of_squares(n, m):
      return sum(i ** 2 for i in range(n, m + 1))