Function make_system_request_span 

pub fn make_system_request_span<B>(req: &Request<B>) -> Span

Create a span for system endpoints (health, metrics, models, engine, loras, etc.).

Same structure as make_inference_request_span but uses target: "system_span" which follows normal DYN_LOG filtering (debug level by default). The inference span target request_span is always-on via a request_span=trace directive; system spans are not, keeping high-frequency polling endpoints quiet.