feat: added skip norm stats

[Skylerwiernik]

Lerobot uses pre/post processing weights instead of norm stats. This allows a user to pass --skip-norm-stats to use an identity matrix.

I used these weights from my lerobot train, with field names converted: https://huggingface.co/s3y/pi05-10-30-openpi/

and ran on my own openpi client. Everything worked as expected.