`known_baseline` lookup so new model architectures don't break existing workers

[tazlin]

I currently rely on the https://github.com/Haidra-Org/horde-worker-reGen/blob/main/horde_worker_regen/_version_meta.json to run betas, but ideally it should be OK to add to the model reference without breaking old workers using meta model load commands such as ALL (causing models that their version can't understand/run).