* fix(fullstack): Streaming::into_inner() returning empty stream
The Streaming struct previously maintained separate input_stream and
output_stream fields, but into_inner() always returned input_stream.
This caused it to return an empty stream on both client and server sides
where data was placed in output_stream.
Consolidate to a single stream field that properly returns the actual
stream data when into_inner() is called.
Also add examples demonstrating bidirectional streaming:
- echo_stream: passes client stream through server unchanged
- transform_stream: transforms client stream on server using filter_map
- Use stream::unfold for cleaner client-side stream generation
Reviewed-by: Claude <noreply@anthropic.com>
Commit-message-by: Claude <noreply@anthropic.com>
* fmt
Ryo Hirayama