Wetterdienst

Feature
- Add retry to functions
- Add IMGW Hydrology API
- Add IMGW Meteorology API

Refactor
- Rename FLOW to DISCHARGE and WATER_LEVEL to STAGE everywhere

Fix
- Fix pyarrow dependency

Refactor
- Backend: Migrate from pandas to polars

Feature
- Sources: Add DWD Road Weather data

Note
- Switching to Polars may cause breaking changes for certain user-space code heavily using pandas idioms, because Wetterdienst now returns a [Polars DataFrame](https://pola-rs.github.io/polars/py-polars/html/reference/dataframe/). If you absolutely must use a pandas DataFrame, you can cast the Polars DataFrame to pandas by using the `.to_pandas()` method.

Fix
- Fix Unit definition for RADIATION_GLOBAL

Fix
- Fix JOULE_PER_SQUARE_METER definition from kilojoule/m2 to joule/m2

Fix
- Update docker images
- Fix now and now_local attributes on core class