DelayedFetchLogOperation will not be trigged to complete when replica number set to 1

### Search before asking

- [x] I searched in the [issues](https://github.com/alibaba/fluss/issues) and found nothing similar.

### Fluss version

0.6.0 (latest release)

### Please describe the bug 🐞

In #768, we directly remove the `tryCompleteDelayedOperations in Replica#appendRecordsToLeader()`:


This may cause `DelayedFetchLogOperation` not be trigged to complete when replica number set to 1 because there are no follower to fetch log from leader and trigger complete `DelayedFetchLogOperation`. In this case, `DelayedFetchLogOperation` will only finished when the wait time timeout.

### Solution

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start by reading Replica#appendRecordsToLeader() and tracing how DelayedFetchLogOperation is completed when the replica count is one. Compare the change referenced from #768 with the delayed-operation flow and verify the fix using the existing replication or fetch-operation tests; done means a single-replica setup completes the fetch without waiting for timeout.

Written by the indexing model from the issue text.