[sgl-router] refactor - move policy-required states under src/state (#40272)

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

experimental/sgl-router/tests/proxy/failover.rs

@@ -54,7 +54,7 @@ async fn failover_when_one_worker_dies() {
             urls: vec![w1.url.clone(), w2.url.clone(), w3.url.clone()],
         }),
         proxy: ProxyConfig::default(),
-        active_load: ActiveLoadConfig::default(),
+        router_inflight_load: InflightLoadConfig::default(),
     };
 
     let tokenizers = Arc::new(TokenizerRegistry::load_from_config(&cfg).unwrap());