Move isinstance checks up a level when reading raw bytes

[greglucas]

Just writing this down for my memory later, but no need to do anything with this now.

Here I think we could put these isinstance checks outside this function so it is only checked once on the initial input stream and not every read.

            if isinstance(source, io.BufferedIOBase):
                byte_reader = source.read
            elif isinstance(source, socket.socket):
                byte_reader = source.recv
        ...
        data = byte_reader(read_size_bytes)

Originally posted by @greglucas in #79 (comment)