Fix type annotation of `MessageData.get_latency`

[lbedogni]

Status: Ready for PR. Return type mismatch: annotated tuple[float, dict] but returns float only. Check message_data.py.

[ff225]

Already fixed on main — MessageData.get_latency is annotated -> float and returns duration_seconds (a float), matching its actual behavior. Fixed in commit f585fe4. Closing as resolved.