[Bug] xarm7_ability robot instability

[dwaitbhatt]

The xArm7 Ability robot added under agents/robots exhibits severe instability during simulation.

Steps to Reproduce:

• Run the demo_robot_script by following these instructions from the documentation
• Use the xarm robot by passing -r xarm7_ability
• Add the --none-actions flag

Expected Behavior:
The robot should move to a configuration (possibly with all joint angles set to 0) and maintain that position indefinitely.

Actual Behavior:
Within 5 steps of simulation, all joint angles rapidly increase and go to NaN, indicating instability or a calculation error.

Possible Cause:
I believe the issue is due to improper tuning of the arm controller parameters (arm stiffness, damping, friction parameters).

I would greatly appreciate any fixes, suggestions for tuning the controller, or insights into other potential problems that might be causing the instability.