Pre-export validation: block on unknown bodies in mappings, warn on unmapped keypoints. Catches errors before they reach stac-mjx. Part of [Milestone 1](https://github.com/users/HugoFara/projects/4). Shipped in #5.
Pre-export validation: block on unknown bodies in mappings, warn on unmapped keypoints. Catches errors before they reach stac-mjx.
Part of Milestone 1.
Shipped in #5.