Function make_inference_request_span 

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

Create a span for inference request endpoints (completions, chat, embeddings, etc.).

Uses target: "request_span" which is always allowed through the DYN_LOG filter (via request_span=trace directive in filters()). This ensures request context (request_id, model, trace_id) is always available on log events.