Test Coverage and CI improvements

[Zeitsperre]

Thanks for submitting a PR, your contribution is really appreciated!

Here's a quick checklist that should be present in PRs (you can delete this text from the final description, this is just a guideline):

• Include documentation when adding new features.
• Include new tests or update existing tests when applicable.

[summarize your pull request here]

Changes

• Split the development requirements into a requirements-dev.txt file, added coverage-related dependencies
• Added a configuration for pytest to run with coverage testing to setup.cfg
• Updated the testing CI main.yml (previously python-app.yml) to perform a development install and check version compatibility
• Added a note in the publishing workflow about deployment environments.

[Zeitsperre]

@huard

To close this, you'll need to change the required checks to remove build (3.10) and set it to require the Coverall Report job. The last step will be to add the Coveralls.io webhook (can be done by going to https://coveralls.io/repos/new and enabling xncml).