[Enhancement✨]  Improve replicas_manager accessor to return Option<&T> in BrokerRuntimeInner

### Current Behavior

<img width="2168" height="1238" alt="Image" src="https://github.com/user-attachments/assets/18aa8d2f-f589-4cde-9807-c6b891f152c0" />

### Proposed Enhancement

<img width="1791" height="856" alt="Image" src="https://github.com/user-attachments/assets/e2039273-d1db-4c89-b981-dff41facb1a1" />

### Benefits

_No response_

### Additional Context

_No response_