input: Write a function to add two large numbers represented as strings. The function should take two string inputs representing the numbers and return their sum as a string.
  assert add_large_numbers("111", "1337")=="1448"
  assert add_large_numbers("9999", "1")=="10000"
  assert add_large_numbers("876", "123")=="999"
  assert add_large_numbers("0", "0")=="0"
  assert add_large_numbers("999", "1001")=="2000"
output: def add_large_numbers(num1, num2):
      return str(int(num1) + int(num2))