No nnfabrik core

[KonstantinWilleke]

It is time. Let's get rid of nnfabrik_core.

This PR would make the use of nnfabrik more straightforward. Now all that is needed to import all main tables would be these lines:

from nnfabrik import my_nnfabrik

main_nnfabrik, Fabrikant, Dataset, Model, Trainer, Seed = my_nnfabrik(
    schema="nnfabrik_neural_prediction_challenge",
    use_common_fabrikant=False,
    return_main_tables=True,
)

@main_nnfabrik.schema
class TrainedModel(TrainedModelBase):
    table_comment = "Trained models"
    nnfabrik = main_nnfabrik

Before that, the cleanest way to import all tables was this:

main_nnfabrik = my_nnfabrik(
    schema="nnfabrik_neural_prediction_challenge",
    use_common_fabrikant=False,
)

Fabrikant, Dataset, Model, Trainer, Seed = map(
    main_nnfabrik.__dict__.get, ["Fabrikant", "Dataset", "Model", "Trainer", "Seed"]
)


@main_nnfabrik.schema
class TrainedModel(TrainedModelBase):
    table_comment = "Trained models"
    nnfabrik = main_nnfabrik

[KonstantinWilleke]

Change Documentation along with it. (Arne's comment)

[KonstantinWilleke]

from nnfabrik import my_nnfabrik

# new default
schema, *tables = my_nnfabrik(schema="my_project_schema")
Dataset, ... = tables

# advanced use case
schemas, *tables = my_nnfabrik(
    schema={
        'my_name': ["Fabrikant", "Dataset", "Model", "Trainer" ], 
        'common_name': ["Seed"],
        }
)
Dataset, ... = tables

[christoph-blessing]

Please request my review again once you made the changes we talked about yesterday.

[mohammadbashiri]

Please request my review once the changes are implemented and the PR can be merged into the main branch without problems.