Prefer byteorder in place of bincode

[frankmcsherry]

Some framing parts of Message<C, T> use bincode to encode u64 data, though byteorder is just as good and may have better alignment properties (it's unclear if bincode ensures alignment, or uses clever varint encoding). This moves us in a direction where there can be more certainty about the shape of serialized data, that would make zero-copy deserialization, which relies on alignment of bytes to be efficient, more likely to work out well.