Adds missing UpgradeResponseParts export

[SirCipher]

Closes #55

[nakedible-p]

FWIW, I can now use the provided function and the code has been tested to work:

            let protocols = ratchet_core::SubprotocolRegistry::new(vec!["xxx"]).expect("creating protocol registry should not fail");
            let provider = if ENV_CONFIG.disable_ws_compression {
                None
            } else {
                let deflate_config = ratchet_deflate::DeflateConfig {
                    server_max_window_bits: ratchet_deflate::WindowBits::try_from(ENV_CONFIG.ws_deflate_server_max_window_bits)
                        .expect("invalid server max window bits"),
                    compression_level: ratchet_deflate::Compression::new(ENV_CONFIG.ws_deflate_level),
                    ..Default::default()
                };
                Some(ratchet_deflate::DeflateExtProvider::with_config(deflate_config))
            };
            let ratchet_core::server::UpgradeResponseParts {
                response,
                subprotocol,
                extension,
                ..
            } = ratchet_core::server::response_from_headers(&parts.headers, provider, &protocols)
                .map_err(|e| RpcError::new(RpcError::BAD_REQUEST, anyhow!(e)))?;
            if subprotocol.is_none() {
                return Err(RpcError::new(
                    RpcError::BAD_REQUEST,
                    anyhow!("no valid websocket protocol selected"),
                ));
            }
            let Some(on_upgrade) = parts.extensions.remove::<hyper::upgrade::OnUpgrade>() else {
                return Err(RpcError::new(
                    RpcError::INTERNAL_ERROR,
                    anyhow!("upgrade handler not found on request"),
                ));
            };

            let mut response = response.map(|_| axum::body::Body::empty());
            // other mutation to response

            // spawn handler that will receive raw stream
            tokio::spawn(async move {
                match on_upgrade.await {
                    Ok(upgraded) => {
                        let upgraded = hyper_util::rt::tokio::TokioIo::new(upgraded);
                        let ws = ratchet_core::WebSocket::from_upgraded(
                            ratchet_core::WebSocketConfig::default(),
                            upgraded,
                            extension,
                            bytes::BytesMut::new(),
                            ratchet_core::Role::Server,
                        );

The custom stuff has been cleaned up from the code so it only shows ratchet relevant bits.

[SirCipher]

@nakedible-p that looks much cleaner. Thanks for all of your feedback