Fix logic used to calculate BinaryValue's lenght

[cherchiga]

While trying to use this library with protobuf, we ran into an issue with the logic used to calculate the lenght of a Bytes type, BinaryValue. The function currently used accept a string and tries to encode it to UTF-8 before calculating the lenght.

def _get_string_size_in_bytes(self, s: str) -> int:
    """
    Responsible for calculating the size of a string in bytes

    :s: The string whose size is to be determined.

    """
    return len(s.encode('utf-8'))

I have created a new method specific for Bytes type that removes the encoding and it passes all the tests.

def _get_bytes_size_in_bytes(self, b: bytes) -> int:
    """
    Responsible for calculating the size of a byte collection in bytes

    :b: The byte collection whose size is to be determined.

    """
    return len(b)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.