added ByteStream protocol

[rimwolf-redux]

Adds ByteStream protocol to circuitpython_typing. Partially addresses #6050 by defining a suitable type for annotating in msgpack.pack and msgpack.unpack.

[dhalbert]

Looks good! I wonder if we want separate Read and Write ByteStreams, for cases where the stream is only read or written to. @prplz suggested that in adafruit/circuitpython#6050? Would that make sense, do you think, to be more precise?

We seem to be ahead of the kinds of things regular Python has added already to their typing protocols.

[rimwolf-redux]

If there's a use case for it, it would be useful to have Readable- and WriteableByteStream. I'll go ahead and make another commit for that.

My only concern is whether we still need the combo ByteStream as a single type annotation; I'm not familiar with other places byte streams are use in CircPy. The obvious thing to do is have a class ByteStream(ReadableByteSteam, WriteableByteStream) definition. But sometimes it seems that readthedocs isn't good about showing either superclasses or inherited methods; I know I've had to guess where to find a description of a method that I know an object has.

[dhalbert]

Let's do this for now, and do more specialized streams on demand, as we need them. It's very easy to add to this library. Thanks!