fix: properly serialize pydantic models

[collindutter]

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Describe your changes

Problem:

Pydantic models are not being handled by our serialization process. This results in events that look like this:

{
│   'type': 'FinishStructureRunEvent',
│   'id': '224441bcb1c449b391576081914dd4a2',
│   'timestamp': 1740425885.337445,
│   'meta': {},
│   'structure_id': None,
│   'output_task_input': None,
│   'output_task_output': {
│   │   'type': 'ModelArtifact',
│   │   'id': '49469681d5c049139a34f95e5bdda990',
│   │   'reference': None,
│   │   'meta': {},
│   │   'name': '49469681d5c049139a34f95e5bdda990',
│   │   'value': Output(text='hello') # not serializable!
│   }
}

Solution:

1. Introduce a ModelArtifact that is used exclusively for wrapping Pydantic models. This should be a non-breaking change since it subclasses GenericArtifact. There are hacks we could use for getting information out of GenericArtifact, but they are hacky and would require non-trivial refactors to implement.

2. During serialization, detect instances of BaseModels and serialize them using a custom marshmallow field, fields.Model. Deserialization for this field has not been implemented at this time as it would require us to somehow store the Pydantic model with the field. I don't think users will run into this during regular usage, but the workaround would be to manually deserialize the Pydantic model outside griptape.

Serialized events now look like:

{
│   'type': 'FinishStructureRunEvent',
│   'id': '8ab4850b69534589a36cc2254612a004',
│   'timestamp': 1740426782.152982,
│   'meta': {},
│   'structure_id': None,
│   'output_task_input': None,
│   'output_task_output': {
│   │   'type': 'ModelArtifact',
│   │   'id': 'b3c96262b9be4d78bb89399321f84f72',
│   │   'reference': None,
│   │   'meta': {},
│   │   'name': 'b3c96262b9be4d78bb89399321f84f72',
│   │   'value': {'text': 'hello'} # serializable!
│   }
}

Issue ticket number and link

Closes #1756
YASW (yet another serialization woe): #1587

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