fix: hanging resources in clear

Author: sophia-bq

common/lib/host_list_provider/monitoring/monitoring_host_list_provider.ts

@@ -52,7 +52,13 @@ export class MonitoringRdsHostListProvider extends RdsHostListProvider {
 
   async clearAll(): Promise<void> {
     RdsHostListProvider.clearAll();
-    await MonitoringRdsHostListProvider.monitors.clear();
+    // TODO: refactor when sliding-expiration-cache refactoring is merged.
+    for (const [key, monitor] of MonitoringRdsHostListProvider.monitors.entries) {
+      if (monitor !== undefined) {
+        await monitor.item.close();
+      }
+    }
+    MonitoringRdsHostListProvider.monitors.clear();
   }
 
   async queryForTopology(targetClient: ClientWrapper, dialect: DatabaseDialect): Promise<HostInfo[]> {