_handle_stream_ended() in async_connection.py (used by the ASGI worker)
did not set stream._body_complete = True or signal stream._body_event.
This caused the receive() closure in protocol.py to never see the body
as complete via the streaming path, so on the next call the fast path
re-read the entire body from BytesIO, doubling it.
The sync handler in connection.py already had a partial fix from #3559
but was also missing _body_event signalling, which is needed to unblock
any pending read_body_chunk() await.
Fixes https://github.com/benoitc/gunicorn/discussions/3567
- Send GOAWAY with correct error codes for protocol violations
- Handle StreamClosedError and FlowControlError gracefully
- Return False instead of raising for missing/closed streams
- Handle flow control window overflow per RFC 7540
- Fix reader race condition and add h2 exception handling
- Wait for WINDOW_UPDATE when flow control window is zero/negative
- Use h2 exception's error_code for INITIAL_WINDOW_SIZE violations
