Employ a src-based layout for code base

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• Tests for the changes have been added (for bug fixes / features)
  • (If applicable) Documentation has been added / updated (for bug fixes / features)
• 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?

• Adapts the code base to use a src-based layout (in lieu of a flat code base layout)
• Added a stricter yamllint configuration (no changes made to existing YAML files)
• Pins pint to >=0.24.4 in order to support Python3.13 (and evade failures from flexparser>=0.4).

Does this PR introduce a breaking change?

Yes. The code base has been modified such that existing interactive (--editable) installations will need to be re-installed.

This change prevents developers from accidentally running tests or importing xclim from the root directory. That's essentially the major gain.

Otherwise, we can say that this brings xclim closer in line with the other Ouranosinc/cookiecutter-pypackage template-based projects.

Other information:

https://packaging.python.org/en/latest/discussions/src-layout-vs-flat-layout/
https://www.pyopensci.org/python-package-guide/package-structure-code/python-package-structure.html#the-src-layout-and-testing

[github-actions]

Note

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

On inspection, the XCLIM_TESTDATA_BRANCH environment variable is set to the most recent tag (v2024.8.23).

No further action is required.

[coxipi]

Looks good to me. Some lines add options (e.g. when cli is invoked, new options I don't know about), and I'm not too familiar with these commands

[Zeitsperre]

The changes to CLI were needed since the location of CHANGELOG.rst can change depending on how the library is installed. It won't necessarily be found two levels above anymore, so passing this file directly via the command line is now permitted.

[coveralls]

coverage: 89.75% (+0.4%) from 89.398%
when pulling ebf4588 on use-src
into d5aefa4 on main.

[aulemahal]

Looks good!