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

### Current Behavior

<img width="2841" height="1662" alt="Image" src="https://github.com/user-attachments/assets/1a15fdf4-c204-4db5-9d63-877352159e98" />

### Proposed Enhancement

<img width="2486" height="1572" alt="Image" src="https://github.com/user-attachments/assets/2d762084-8cb4-45e2-9ff8-65b98a525cf4" />

### Benefits

_No response_

### Additional Context

_No response_