add method stubs in basic in-memory repository

src/repositories/UnoptimizedInMemoryRepository.ts

@@ -58,6 +58,12 @@ export class UnoptimizedInMemoryRepository implements GetterSetterRepository {
     return this.etas.filter(eta => eta.stopId === stopId);
   }
 
+  public async subscribeToEtaChanges(listener: (eta: IEta) => void): Promise<void> {
+  }
+
+  public async unsubscribeFromEtaChanges(listener: (eta: IEta) => void): Promise<void> {
+  }
+
   public async getEtaForShuttleAndStopId(shuttleId: string, stopId: string) {
     return this.findEntityByMatcher<IEta>((value) => value.stopId === stopId && value.shuttleId === shuttleId, this.etas);
   }