sodym pydantic class with default model_config

[JakobBD]

Instead of classes inheriting from pydantic BaseClass, we could make a SodymPydanticModel class, with a default config such as

    model_config = ConfigDict(arbitrary_types_allowed=True, protected_namespaces=(), extra='forbid')

• The first argument would mean we don't have to add it manually everywhere we use non-standard types
• The second argument solves sphinx errors, as suggested in this very helpful comment ;-)
• The third may be the most debatable. I find extras=ignore a bit dangerous, since typos are not caught if the fields have default values. This is especially dangerous if we load class arguments from a dict, such as from the yml config file. In some classes, we add attributes later on, so we are setting extras=allow there, which would create a conflict. Happy to discuss this.