input: Write a python function to encode and decode a string using base64.
  assert encode("Hello World!") == "SGVsbG8gV29ybGQh"
  assert decode("SGVsbG8gV29ybGQh") == "Hello World!"
  assert encode("Python is fun!") == "UHl0aG9uIGlzIGZ1biE="
  assert decode("UHl0aG9uIGlzIGZ1biE=") == "Python is fun!"
output: import base64
  
  def encode(input_string):
      encoded_bytes = base64.b64encode(input_string.encode('utf-8'))
      return encoded_bytes.decode('utf-8')
  
  def decode(encoded_string):
      decoded_bytes = base64.b64decode(encoded_string.encode('utf-8'))
      return decoded_bytes.decode('utf-8')