input: Write a python function to print all key-value pairs in a dictionary.
  assert print_key_value_pairs({'a': 1, 'b': 2, 'c': 3}) == 'a: 1\nb: 2\nc: 3\n'
  assert print_key_value_pairs({'key1': 'value1', 'key2': 'value2'}) == 'key1: value1\nkey2: value2\n'
  assert print_key_value_pairs({}) == ''
output: def print_key_value_pairs(d):
      result = ""
      for key, value in d.items():
          result += f"{key}: {value}\n"
      return result