Integrate xlerobot into lerobot stack

[AntoniBertel]

What this does

• Adds support for both 2‑bus and 4‑bus xlerobot layouts
• Unified the host/client keyboard path with BaseKeyboardController
• General improvements and refactoring, including instructions on mapping each logical bus role to a /dev/<alias> by servo serial number (see xlerobot_config.py, “Map of logical bus roles to device ports”) so users can create stable udev rules for each controller

How it was tested / How to try it

• With lerobot-teleoperate

• Run as any other lerobot devices for example

python -m lerobot.robots.xlerobot.xlerobot_host --robot.id=xlerobot_debug

and

lerobot-teleoperate \
  --robot.type=xlerobot_client \
  --robot.id=xlerobot_debug \
  --robot.remote_ip=127.0.0.1 \
  --teleop.type=keyboard \
  --teleop.id=keyboard1 \
  --display_data=true

[AntoniBertel]

@CarolinePascal @imstevenpmwork @jadechoghari please take a look when you have a moment