`model_version` parameter of `Simulation` conflicts with Pydantic reserved keywords

[anth-volk]

Pydantic reserves all keywords beginning with model_, and our model_version keyword conflicts with that. We could do any of the following:

1. Rename it and modify API v2 and the main API to use a new arg (not ideal)
2. Within the schema, write a function to automatically remap model_version to a stand-in
3. Override Pydantic's settings to allow model_ args (not ideal)