✅ Wave 112 Agent 14: Fix failing api_gateway tests

- Added #[tokio::test] to test_circuit_breaker_check (runtime fix)
- Verified constant_time_compare security (already correct)
- All 64 tests now passing (was 62/64)

services/api_gateway/src/grpc/trading_proxy.rs

@@ -521,8 +521,8 @@ mod tests {
         assert!(!checker.is_healthy());
     }
 
-    #[test]
-    fn test_circuit_breaker_check() {
+    #[tokio::test]
+    async fn test_circuit_breaker_check() {
         let checker = Arc::new(HealthChecker::new(30));
         let proxy = TradingServiceProxy {
             client: TradingServiceClient::new(