`StreamTrait::now()` should be fallible

[LastExceed]

Stream handles can become invalid (ErrorKind::StreamInvalidated), and an invalidated stream should not have to return valid stream timestamps.

[roderickvd]

I don’t know about that. An invalid stream can still have a perfectly valid clock, and on most backends it returns a monotonic host clock.

It could be that the host dies (particularly with audio servers like PipeWire or JACK) in which case we could just stop the clock from increasing, if that’s not what we’re doing already.