Add lightinig randomization to RosGrpcScene

### Description

Introduced in #137, we are waiting for the gRPC API extension from our trainees, to control the [`wled_ros_driver`](https://github.com/AGH-CEAI/wled_ros_driver)

### References

_No response_

Start by locating RosGrpcScene and reviewing the gRPC API extension expected from wled_ros_driver; the issue says implementation is waiting on that extension. Confirm the API contract and intended lighting-randomization behavior with maintainers, then verify that randomization works through the scene.

Rédigé par le modèle d'indexation à partir du texte de l'issue.