restrict rule 'build_existing_chp_de' memory for reliable PyPSA-AT testruns

[pworschischek-aggmag]

Before asking for a review for this PR make sure to complete the following checklist:

• Workflow with target rule ariadne_all completes without errors
• The logic of export_ariadne_variables has been adapted to the changes
• One or several figures that validate the changes in the PR have been posted as a comment
• A brief description of the changes has been added to Changelog.md
• The latest main has been merged into the PR
• The config has a new prefix of the format YYYYMMDDdescriptive_title

A minor change to prevent PyPSA-AT CI tests from failing with <Signals.SIGTERM: 15> (=out of memory) in rule build_existing_chp_de. Here is an example for a failed testrun due to memory problems. Setting a resource limit for build_existing_chp_de fixes the issue.

Sorry, I did not run the full PyPSA-DE workflow. If you require more checked boxes, let me know and I'll see to it in the next couple of days.

[pworschischek-aggmag]

I see that the PyPSA-DE pipeline fails due to out-of-space errors. I fixed that for PyPSA-AT with

    - name: Free Disk Space (Ubuntu)
      uses: jlumbroso/free-disk-space@main
      with:
        # Remove tools that are not needed
        tool-cache: false
        android: true
        dotnet: true
        haskell: true
        large-packages: false
        docker-images: true
        swap-storage: true

The action frees up ~21 GB disk space on the runner VM and takes around 30 seconds to complete. This PR does not contain this fix!

Furthermore, I migrated all tests to pixi for simplicity. Python packages are not cached anymore and install using the pixi.lock within ~30 sec. The benefit is a radically simplified workflow.

[lindnemi]

I see that the PyPSA-DE pipeline fails due to out-of-space errors. I fixed that for PyPSA-AT with

    - name: Free Disk Space (Ubuntu)
      uses: jlumbroso/free-disk-space@main
      with:
        # Remove tools that are not needed
        tool-cache: false
        android: true
        dotnet: true
        haskell: true
        large-packages: false
        docker-images: true
        swap-storage: true

The action frees up ~21 GB disk space on the runner VM and takes around 30 seconds to complete. This PR does not contain this fix!

Furthermore, I migrated all tests to pixi for simplicity. Python packages are not cached anymore and install using the pixi.lock within ~30 sec. The benefit is a radically simplified workflow.

This sounds very promising! @lkstrp could you take a look?