fix(gateway): 修复 balance 刷新去重键冲突、usage 状态回退与测试竞态

- balance_cache: 引入实例级 refresh key 防止多实例共享进程级 HashSet 冲突
- InMemoryUsageRepo: 阻止 pending/streaming 状态覆盖已终结(completed/failed/cancelled)记录
- usage 同步测试: 等待条件从 is_some() 改为检查 status=="completed" 避免竞态
- wallet 测试: 增加轮询等待 wallet 扣款完成
- 整理 import 语句与 tests 模块位置

apps/aether-gateway/src/tests/usage/direct.rs

@@ -111,7 +111,10 @@ async fn gateway_records_usage_for_execution_runtime_sync_when_runtime_enabled()
             .find_by_request_id("req-usage-sync-123")
             .await
             .expect("usage lookup should succeed");
-        if stored.is_some() {
+        if stored
+            .as_ref()
+            .is_some_and(|usage| usage.status == "completed")
+        {
             break;
         }
         tokio::time::sleep(std::time::Duration::from_millis(10)).await;