Raise timeout exception from async stream

[flacjacket]

Using httpx, the .stream method does not raise an exception when the
device goes offline if the read timeout is disabled. To get around this,
introduce a new exception that will be thrown if a timeout is hit so it
can more easily be handled and the stream reconnected as needed. Add
handling logic to the async_event_stream so it behaves like the
non-async method by retrying while read errors are thrown.