Fix handling of inactive storage components in constraints/variables

[Irieo]

Closes #1440

Changes proposed in this Pull Request

This PR fixes two problems related to active/inactive attr handling. First was connected to xarray alignment error when some storage components have active=False due to unfiltered data arrays being combined with filtered variables. Second was connected to spillage variable fail when all StorageUnits are inactive due to empty array issue.

Thanks @SpamAndEgg for spotting these.

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in docs.
• Unit tests for new features were added (if applicable).
• A note for the release notes docs/release-notes.md of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.