support pydantic v2

[visr]

I went a few steps further than mentioned in #382 (comment), but I get stuck, so it is probably better to continue after #630.

Main issues are that these nested default dicts are not appreciated by mypy: 50cf27f#diff-bdece7de80ef751956236e71b5aed3964311d59479f076c892d6745b0e30266d

The other one is that it doesn't like the optional DataFrame:

>       node = ribasim.Node(
            static=gpd.GeoDataFrame(
                data={
                    "type": node_type,
                    "name": [ribasim.utils.random_string() for _ in range(len(node_id))],
                },
                index=pd.Index(node_id, name="fid"),
                geometry=node_xy,
                crs="EPSG:28992",
            )
        )
E       pydantic_core._pydantic_core.ValidationError: 1 validation error for Node
E       static
E         Value error, Cannot use DataFrame as a pydantic type as its DataFrameModel cannot be converted to a DataFrameSchema.
E       Please revisit the model to address the following errors:
E       Found missing annotations: ['model_config'] [type=value_error, input_value=                     type...vc   POINT (6.000 1.000), input_type=GeoDataFrame]
E           For further information visit https://errors.pydantic.dev/2.4/v/value_error

python\ribasim_testmodels\ribasim_testmodels\basic.py:160: ValidationError

Would fix #382.

[evetion]

I'll take over this branch in #731, thank you very much.