Skip json dump

[emilhe]

The json dump change the object from a BaseModel instance, which hinders e.g. custom rendering of accordion title. Here is a small example where the title is a json dump in the current code (with the json dump), while it renders correctly with the callsign as title when the json dump is remove (this PR),

from enum import Enum

import dash
import dash_mantine_components as dmc
from dash import Dash, Input, callback
from pydantic import BaseModel
from rich import print

from dash_pydantic_form.model_form import ModelForm

class PetType(Enum):
    DOG = "dog"
    CAT = "cat"

class Pet(BaseModel):
    callsign: str
    pet_type: PetType

    def __str__(self) -> str:
        return self.callsign

class PetClub(BaseModel):
    members: list[Pet]

dash._dash_renderer._set_react_version("18.2.0")  # type: ignore
app = Dash()
app.layout = dmc.MantineProvider(
    ModelForm(
        PetClub(
            members=[
                Pet(callsign="Thunder bark", pet_type=PetType.DOG),
                Pet(callsign="Lightning meow", pet_type=PetType.CAT),
            ]
        ),
        aio_id="pet_club",
        form_id="my_pet_club",
    )
)

@callback(Input(ModelForm.ids.main("pet_club", "my_pet_club"), "data"))
def on_form_change(data):
    print(data)

if __name__ == "__main__":
    app.run_server(debug=False, port=8888)

The example also includes an Enum field to demonstrate that the change does not cause issues with enums.