This makes all Torax Pydantic models frozen to allow safe use of functools.cached_property. A special method update_fields is added to the top-level model ToraxConfig, which allows users to safely update fields whilst invalidating the minimal set of caches (ie. the current model along with all ancestral models). update_fields is not safe to call for submodels of ToraxConfig, hence making this private (but still accessible if a user really wants/needs to use it).

This makes all Torax Pydantic models frozen to allow safe use of functools.cached_property. A special method update_fields is added to the top-level model ToraxConfig, which allows users to safely update fields whilst invalidating the minimal set of caches (ie. the current model along with all ancestral models). update_fields is not safe to call for submodels of ToraxConfig, hence making this private (but still accessible if a user really wants/needs to use it). #5113