input: Write a python function to pad bytes to a specified length divisible by a given multiple.
  assert pad_bytes(b'hello', 4) == b'hello\x00\x00\x00'
  assert pad_bytes(b'hello', 8) == b'hello\x00\x00\x00'
  assert pad_bytes(b'helloworld', 8) == b'helloworld\x00\x00'
output: def pad_bytes(data, multiple):
      padding_needed = (multiple - len(data) % multiple) % multiple
      return data + b'\x00' * padding_needed