Describe your changes

This PR makes sure static features are standardized in the same way as state and forcing. As standard features are loaded directly in the model, they are not handled by the standardization in WeatherDataset. This makes sure that they are still standardized.

The standardization is achieved by introducing an optional argument standardize in the get_dataarray Datastore method, optionally returning the dataarray standardized. The motivation is to leave as much of the control of the data loading to the Datastore class. It is also good to have this re-usable approach, as the same standardization method can then later be used for loading static fields in the boundary region.

In the future also other types of rescaling (e.g. to [0,1]) might be desirable for static features as well as making standardization optional. However, as that similarly applies to state and forcing that is a separate issue.

Issue Link

This closes #95.

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📖 Documentation (Addition or improvements to documentation)

Checklist before requesting a review

• My branch is up-to-date with the target branch - if not update your fork with the changes from the target branch (use pull with --rebase option if possible).
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• the code is readable
• the code is well tested
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• I have added a line to the CHANGELOG describing this change, in a section
  reflecting type of change (add section where missing):
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  • changed: when default behaviour of the code has been changed
  • fixes: when your contribution fixes a bug

Checklist for assignee

• PR is up to date with the base branch
• the tests pass
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