input: Write a python function to generate and return the squares of numbers from 1 to n in string format.
  assert generate_squares_string(5) == ['1', '4', '9', '16', '25']
  assert generate_squares_string(3) == ['1', '4', '9']
  assert generate_squares_string(0) == []
output: def generate_squares_string(n):
      return [str(i * i) for i in range(1, n + 1)]