feat: add SO101 operator-interface teleop support

[juelg]

Summary

• add an SO101 operator and config for the operator interface introduced in feat: operator interface #264
• add a lazy SO101 leader helper in the SO101 extension
• add a hardware-free SO101 operator test module and a teleop example script

Validation

• black python/rcs/operator/so101.py python/tests/test_so101_operator.py examples/teleop/so101.py extensions/rcs_so101/src/rcs_so101/creators.py extensions/rcs_so101/src/rcs_so101/init.py python/rcs/operator/init.py
• isort python/rcs/operator/so101.py python/tests/test_so101_operator.py examples/teleop/so101.py extensions/rcs_so101/src/rcs_so101/creators.py extensions/rcs_so101/src/rcs_so101/init.py python/rcs/operator/init.py
• ruff check python/rcs/operator/so101.py python/tests/test_so101_operator.py examples/teleop/so101.py extensions/rcs_so101/src/rcs_so101/creators.py extensions/rcs_so101/src/rcs_so101/init.py python/rcs/operator/init.py
• python -m pytest python/tests/test_so101_operator.py

Closes #273