fn dirty_epochs(&self, object_id: ObjectId) -> Vec<FlushEpoch> {
        let mut dirty_epochs = vec![];
        let flush_model = self.flush_model.lock().unwrap();

        let active_epochs = flush_model
            .range((object_id, FlushEpoch::MIN)..=(object_id, FlushEpoch::MAX));

        for ((_oid, epoch), history) in active_epochs {
            let (last_state, _at) = history.last().unwrap();
            if last_state.needs_flush() {
                dirty_epochs.push(*epoch);
            }
        }

        dirty_epochs
    }
Returns the FlushEpochs for which this ObjectId has unflushed
dirty data for.
src/event_verifier.rs