Add velocity visualization (ground truth & predictions) in visualize_nusc.py

[DavideSecco]

It would be extremely helpful to visualize both ground truth and predicted velocities in the Bird's-Eye View (BEV) within `` visulize_nusc.py` . Specifically, I suggest:

• Drawing an arrow to represent each object's velocity (both GT and predicted).

• Displaying the velocity value (magnitude) next to each arrow.

This feature would make it easier to compare ground truth velocities with the predicted ones, especially for moving objects, and gain better insight into the accuracy of velocity estimation.

Thank you! If anyone has ideas or wants to implement this, I'd be very interested to see it.