(Scoped)SubscriptionHandle to unsubscribe from memory updates

Implements SubscriptionHandle returned by MemoryListener::subscribe() to unsubscribe from memory via SubscriptionHandle::release() or MemoryListener::unsubscribe(SubscriptionHandle handle) at a later point in time. Further implements ScopedSubscriptionHandle which is move-assignable via a SubscriptionHandle and automatically unsubscribes when running out of scope.

Needed for sw/armarx/skills/speech!4 (merged) (see sw/armarx/skills/speech!4 (comment 64668))

source/RobotAPI/libraries/armem/client/util/SubscriptionHandle.h

@@ -57,4 +57,6 @@ namespace armarx::armem::client::util
         SubscriptionHandle handle;
     };
 
+    void swap(SubscriptionHandle& first, SubscriptionHandle& second);
+
 } // namespace armarx::armem::client::util