👷♻️ Improved Reusable Workflows

[burgholzer]

Description

This PR refactors parts of the reusable workflow and enhances them. Notable changes:

• ⚡ Build and test parallelism is increased. Most public GitHub runners offer 4 cores now.
• 🚸 Slightly reduces the number of individual macOS runs to avoid hitting the concurrency limit of 5 runners too often.
• ✨ Adjusts the Python packaging workflow so that it also applies to pure Python projects
• 🚸 Makes the default GitHub token available to Python test runs
• ♻️ Combines the Python test and minimal version runs. This means fewer workflow runs and fewer coverage uploads. Minimal versions are now tests on all Python versions and operating systems to ensure smooth operation of the resulting packages.
• ♻️ Automates the Python version selection for building wheels. Just one less place to touch when a new Python version comes around.

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.4%. Comparing base (cb555c9) to head (ad8d582).

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #594   +/-   ##
=====================================
  Coverage   91.4%   91.4%           
=====================================
  Files        131     131           
  Lines      14090   14090           
  Branches    2249    2249           
=====================================
+ Hits       12885   12886    +1     
+ Misses      1205    1204    -1     

Flag	Coverage Δ
cpp	91.1% <ø> (+<0.1%)	⬆️
python	99.7% <ø> (ø)

see 1 file with indirect coverage changes