WIP: added small smoke test

[mcocdawc]

Description

Since xarray is supposed to be optional, the failing imports should be caught gracefully.

In addition, xarray is removed from the test category of the pyproject.toml, as it is not necessary for the test pipeline.
Testing with all optional dependencies requires installing with pip install '.[all]'.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.