Tune qpos-only robot drive dynamics

[yuecideng]

Description

This PR tunes the qpos-only default drive dynamics for Franka Panda, UR10e, CobotMagic, and DexForce W1. It adds an executable four-robot trajectory benchmark and configuration regression coverage.

The benchmark sends only qpos targets at 60 Hz against a 240 Hz physics step; it records any qvel-target writes and fails the qpos-only contract if one occurs.

Dependencies: none.

Type of change

• Bug fix (non-breaking change which fixes qpos-only tracking)
• Enhancement
• New feature
• Breaking change
• Documentation update

Validation

• Black formatting: passed (829 files unchanged).
• Public API documentation gate: passed (1672/1672 exports documented).
• Configuration regression test: pytest tests/sim/objects/test_robot_drive_defaults.py -q (4 passed).
• Full simulator benchmark: 60 Hz qpos-only commands, 240 Hz physics, 1 s hold, 3 s sine trajectory, CUDA. All qvel-target write counts were zero.

Robot	Normalized RMSE	Normalized P95	Static normalized RMSE
Franka Panda	0.017	0.035	0.011
UR10e	0.066	0.163	0.064
CobotMagic	0.019	0.034	0.002
DexForce W1	0.023	0.041	0.007

Tracking thresholds: normalized RMSE <= 0.10, normalized P95 <= 0.20, static normalized RMSE <= 0.10.

Checklist

• I have run Black formatting.
• Sphinx documentation changes are not applicable.
• Public API documentation coverage is verified.
• I have added tests that prove the configuration defaults.
• Dependencies have not changed.