[FEATURE] use data_types in python core

[mgovers]

This will help users provide the correct data types to the power grid model

Context

The data types are now declared in the user-level module, but would also be really useful in the core. In addition, there are a couple other things that are useful both in the core and for users, namely (this is already done):

• src/power_grid_model/data_types.py
• the functionality included from _utils into utils.py

TODO

• [ ] above topics should be moved to power_grid_model.core or otherwise made private to the module by prefixing with _ and then imported in the public interface and then included in the API reference.
• [ ] Ensure they are still present in the API reference under the same name as the public functionality
  • [ ] Sphinx autodoc only works on the module level (with the imported_members option enabled); or
  • [ ] otherwise __all__ should be filled with everything discoverable in the API to enable listing them in the API reference
• [ ] make sure that the python core uses the data types declared in data_types.py