Fixes tensor construction warning in events.py

[louislelay]

Description

This PR removes a UserWarning from PyTorch about using torch.tensor() on an existing tensor in events.py. It replaces torch.tensor(actuator.joint_indices, device=asset.device) with .to(device) to avoid unnecessary copies.

Warning mentionned:

/home/spring/IsaacLab/source/isaaclab/isaaclab/envs/mdp/events.py:542: 
UserWarning: To copy construct from a tensor, it is recommended to use sourceTensor.clone().detach() or sourceTensor.clone().detach().requires_grad_(True), rather than torch.tensor(sourceTensor). actuator_joint_indices = torch.tensor(actuator.joint_indices, device=asset.device)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[ooctipus]

@louislelay

So actuator.joint_indices can only be torch.tensor or slice? if that is true maybe add if isinstance(slice), elif isinstance(torch.Tensor), else raise error may be a bit more readable?

On a second note, do you think check the type during call time can be too expensive (I know you didn't write the original function, so no pressure to edit), (◎ ◎)ゞ why couldn't we do the check and construct indices during init construction instead?

Would love to know your thought on it. : ))