Refactor robots

[aliberts]

What this does

• Replaces all form-factor-based abstractions by a single and simpler Robot base class.
• Splits Robot abstraction into separate Robot and Teleoperator.
• Each robot gets its own directory where its code, config and docs live, similar to policies.
• All robot-related code only use simple np.ndarrays for data (no more torch.Tensor).
• Default calibration directory move to ~/.cache/huggingface/lerobot/.calibration. Also configurable with the HF_LEROBOT_CALIBRATION env variable.
• More to come

How it was tested

TODO

How to checkout & try? (for the reviewer)

TODO