Before Creating the Enhancement Request

• I have confirmed that this should be classified as an enhancement rather than a bug/feature.

Summary

Currently, TimerMessageReputService creates an internal ThreadPoolExecutor
with hard-coded parameters and does not explicitly shut it down during broker shutdown, which may cause thread resources to be retained longer than expected.

This PR makes the executor configuration configurable and ensures it is
shutdown gracefully when the service stops.

Motivation

null

Describe the Solution You'd Like

1. make some config configurable
2. shutdown inner executor when broker shutdown

Describe Alternatives You've Considered

null

Additional Context

No response