test(data-streams): cover transcription tap fan-out
These tests show that two consumers of one transcription stream both get all of the data.
The first test registers an application handler and listens for the event. Both consumers get the
full text.
The second test sends the payload inside the header packet. This is a single-packet stream. Both
consumers get the full text.
The third test sends a trailer that sets the lk.transcription_final attribute. Both readers see
the new attribute value. This shows that the consumers share one info object.
