Python support: drop support for Python 3.11

[mgovers]

NOTE: do not merge before:

• Blockers
  • Follow-ups to add python3.14 release schedule to release.md .github#75 are done:
    • PR merged
    • Important readthedocs builds have been rebuilt (stable, latest and most recent version tag for PGM, PGM-IO and PGM-DS)
  • PGM-DS PR to add support for python 3.14:
    • reviewed + approved + merged Python support: add support for 3.14 power-grid-model-ds#130
    • released in patch version
• Removing support for python 3.11:
  • .github PR has been reviewed + approved: Python support: drop support for python 3.11 .github#76
  • PGM PR has been reviewed + approved: Python support: drop support for Python 3.11 #1261
  • PGM-IO PR has been reviewed + approved: Python support: drop support for Python 3.11 power-grid-model-io#361
  • PGM-DS PR has been reviewed + approved: Python support: drop support for python 3.11 power-grid-model-ds#132

Closes #1230

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[TonyXiang8787]

@mgovers why is a new patch release of pgm-ds needed to push the drop of 3.11 in PGM core?

The pgm-ds is already supporting 3.14. It was not tested in the CI. Now it is tested in the CI. But a new patch version is not needed right? User can already install current pgm-ds in Python 3.14.

EDIT:
They actually have hard upper bound on python versions. Then we do need a patch release...