Cookiecutter update, drop black and isort

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Updates the cookiecutter template to use newer dependencies and conventions
• Drop black and isort (redundant via ruff)
• Remove handling for obsolete owslib
• Tests are now linted (less strictly)

Does this PR introduce a breaking change?

Somewhat. Code style conventions are different, but code is largely the same, barring a handful of small suggested changes.

Other information:

This probably doesn't require a minor release.

[github-actions]

Note

It appears that this Pull Request modifies the main.yml workflow.

On inspection, the RAVEN_TESTDATA_BRANCH environment variable is set to the most recent tag (v2025.6.12).

No further action is required.

[tlvu]

Not sure I can review this. I don't know this repo well enough. I can rubber stamp if you are blocked and need this one in, if that is your intention.

[Zeitsperre]

Not needed. It would be good to get an actual review on this. There's still one strange error happening, but I hope it isn't something broken upstream.

[coveralls]

coverage: 80.779% (+0.03%) from 80.752%
when pulling 01cb0b5 on update-cookiecutter
into 74093f3 on master.