Function send_empty_request 

pub async fn send_empty_request(
    method: Method,
    url: impl Into<String>,
    api_key: impl AsRef<str>,
    config: Arc<HttpClientConfig>,
) -> ZaiResult<Response>

Send a request without a JSON body through the shared transport pipeline.

Always emits a trace line for the outbound request line (no body to log), so GET/DELETE traffic is observable with RUST_LOG=trace.