[model-gateway] minor code clean up (#15578)

sgl-model-gateway/src/core/worker_registry.rs

@@ -122,13 +122,9 @@ impl WorkerRegistry {
     }
 
     /// Reserve (or retrieve) a stable UUID for a worker URL.
+    /// Uses atomic entry API to avoid race conditions between check and insert.
     pub fn reserve_id_for_url(&self, url: &str) -> WorkerId {
-        if let Some(existing_id) = self.url_to_id.get(url) {
-            return existing_id.clone();
-        }
-        let worker_id = WorkerId::new();
-        self.url_to_id.insert(url.to_string(), worker_id.clone());
-        worker_id
+        self.url_to_id.entry(url.to_string()).or_default().clone()
     }
 
     /// Best-effort lookup of the URL for a given worker ID.