CHILLED code needs to be cleaned up

[measrainsey]

As pointed out by @glatterf42 in #18 (review), the CHILLED code would benefit from the following upgrades:

Code could still be cleaned up (e.g. by adding mypy and ruff like we have them in message_ix and addressing linting/formatting errors or by cleaning up comments and type: ignore statements), but this could also happen in a later PR. If saved for later, please open an issue to not forget about this.

This issue is meant to track this work that needs to be done.

[measrainsey]

Making a note that I should really reconfigure the message_ix_buildings.chilled.core.climate.create_climate_variables_maps function because right now the complexity of that function is 39.