Constrain every efuel trade link individually

[lindnemi]

This is one of several branches that I started in parallel to get the final results, and the one that happened to run to 2045 in the end. The bug that was preventing the other branches from running was related to the pypsa version, not the changes.

This branches adresses the problem of efuel exports in a softer manner. Instead of a ban on efuel exports, it implements the efuel import constraints for every carrier separatedly. In this way it prevents, that in the case of an active upper constraint on efuel imports, the model starts to export e.g. biogas in order import more biofuels (because previously export and imports of different efuels cancelled out). The somewhat inexplicable Fisher-Tropsch exports in 2035/40 remain however.

Addtionally this PR does some housekeeping.

Before:


After:

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