fix(rebot-b601): add max_relative_target and Seeed gripper torque limits to B601-RS

[alfieroddan]

Summary

Brings ReBotB601RS in line with the Seeed LeRobot B601-RS follower.

• Add max_relative_target, matching ReBotB601DM (closes reBot B601 RS has no max_relative_target #305). The limit is in joint degrees and scaled by each joint's direction factor, so the 6x gripper gets a matching step
• Gripper torque limit is 3.5 N·m while moving and 1.0 N·m once stalled, down from a flat 10 N·m. Torque is cut if the gripper stalls while opening (closes reBot B601 RS gripper torque limit and feedback #304)
• Reject non-finite gripper gains and torque limits
• teleop-rs.yaml: run at 60 fps, matching lerobot-teleoperate, and set max_relative_target: 10.0

Behaviour change: the default gripper torque limit drops from 10 to 3.5 N·m.

#303 and #306 are unchanged here: the Seeed RS follower also reports torques in the motor frame and uses the same gains.

[Copilot]

Copilot review overview

🟡 Changes recommended

Target scaling, timing, validation, and feedback-failure handling contain unresolved safety-related issues.

Review effort: Balanced
Findings: 1 · 3

Open (4)

• Disable gripper safely when feedback fails · New
• Reject non-finite gripper gains and limits · New
• Scale relative target limits by joint direction · New
• Compute stall velocity using measured control intervals · New

What changed in this PR

Adds B601-RS motion limiting and safer gripper torque behavior.

Changes:

• Adds relative-target limiting and stall-aware gripper torque control.
• Adds corresponding unit tests.
• Updates RS teleoperation to 60 FPS with a 10-degree step limit.

File	Description
tests/​test_rs.py	Tests torque limits, stall cutoff, and target clamping.
src/​physicalai_rebot_b601_plugin/​rs.py	Implements the new safety behavior.
examples/​runtime/​teleop-rs.yaml	Configures 60 FPS and relative-target limiting.

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