feat(bin): support combined up- and download benchmark

[mxinden]

Today, when a server receives a POST, it will read all data off the stream till the end, and then close the stream, sending nothing but a 200 in return.

neqo/neqo-bin/src/server/http3.rs

Lines 156 to 170 in 7c7f1c3

	Http3ServerEvent::Data { stream, data, fin } => {
	if let Some(received) = self.posts.get_mut(&stream) {
	*received += data.len();
	}
	if fin {
	if let Some(received) = self.posts.remove(&stream) {
	let msg = received.to_string().as_bytes().to_vec();
	stream
	.send_headers(&[Header::new(":status", "200")])
	.unwrap();
	stream.send_data(&msg).unwrap();
	stream.stream_close_send().unwrap();
	}
	}
	}

In case the client requested a response via the /<some-number-of-bytes-to-respond-with> pattern, the server ignores it.

neqo/neqo-bin/src/server/http3.rs

Lines 123 to 124 in 7c7f1c3

	} else if let Ok(count) =
	path.value().trim_matches(|p| p == '/').parse::<usize>()

In other words, neqo-bin/src/server/http3.rs does not support a combined up- and download.

Fixing this, I assume, is more about eliminating this pitfall than about providing value through a combined upload and download benchmark.