Tiny refactor select_workers API for future passing more information (#15596)

sgl-model-gateway/tests/cache_aware_backward_compat_test.rs

@@ -2,7 +2,7 @@ use std::{collections::HashMap, sync::Arc};
 
 use sgl_model_gateway::{
     core::{BasicWorkerBuilder, Worker, WorkerType},
-    policies::{CacheAwareConfig, CacheAwarePolicy, LoadBalancingPolicy},
+    policies::{CacheAwareConfig, CacheAwarePolicy, LoadBalancingPolicy, SelectWorkerInfo},
 };
 
 #[test]
@@ -40,7 +40,12 @@ fn test_backward_compatibility_with_empty_model_id() {
     let workers: Vec<Arc<dyn Worker>> = vec![Arc::new(worker1.clone()), Arc::new(worker2.clone())];
 
     // Select worker - should work without errors
-    let selected = policy.select_worker(&workers, Some("test request"));
+    let selected = policy.select_worker(
+        &workers,
+        &SelectWorkerInfo {
+            request_text: Some("test request"),
+        },
+    );
     assert!(selected.is_some(), "Should select a worker");
 
     // Remove workers - should work without errors
@@ -97,12 +102,15 @@ fn test_mixed_model_ids() {
 
     let default_workers: Vec<Arc<dyn Worker>> =
         vec![Arc::new(worker1.clone()), Arc::new(worker3.clone())];
-    let selected = policy.select_worker(&default_workers, Some("test request"));
+    let info = SelectWorkerInfo {
+        request_text: Some("test request"),
+    };
+    let selected = policy.select_worker(&default_workers, &info);
     assert!(selected.is_some(), "Should select from default workers");
 
     let llama_workers: Vec<Arc<dyn Worker>> =
         vec![Arc::new(worker2.clone()), Arc::new(worker4.clone())];
-    let selected = policy.select_worker(&llama_workers, Some("test request"));
+    let selected = policy.select_worker(&llama_workers, &info);
     assert!(selected.is_some(), "Should select from llama-3 workers");
 
     let all_workers: Vec<Arc<dyn Worker>> = vec![
@@ -111,7 +119,7 @@ fn test_mixed_model_ids() {
         Arc::new(worker3.clone()),
         Arc::new(worker4.clone()),
     ];
-    let selected = policy.select_worker(&all_workers, Some("test request"));
+    let selected = policy.select_worker(&all_workers, &info);
     assert!(selected.is_some(), "Should select from all workers");
 }
 
@@ -144,6 +152,11 @@ fn test_remove_worker_by_url_backward_compat() {
     policy.remove_worker_by_url("http://worker1:8080");
 
     let workers: Vec<Arc<dyn Worker>> = vec![Arc::new(worker2.clone())];
-    let selected = policy.select_worker(&workers, Some("test"));
+    let selected = policy.select_worker(
+        &workers,
+        &SelectWorkerInfo {
+            request_text: Some("test"),
+        },
+    );
     assert_eq!(selected, Some(0), "Should only have worker2 left");
 }