Run Python 3.13 testbank

[veenstrajelmer]

First pre-release is available at the end of October according to https://peps.python.org/pep-0719/#schedule, final in October 2024:
3.13.0 alpha 1: Tuesday, 2023-10-17
Expected:
3.13.0 final: Tuesday, 2024-10-01

Github available versions: https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json

Testbank fails because of:

• ERROR: No matching distribution found for numpy>=2.0.0.dev0: Pip module fails to build with Python 3.13 numpy/numpy#24318 and cannot install numpy on python 3.13 numpy/numpy#25917 >> numpy will support python 3.13 approximately from may 2024
• retried on 1-5-2024, now failing on scipy with ../scipy/meson.build:163:9: ERROR: Dependency "OpenBLAS" not found, tried pkgconfig and cmake. The numpy issue was closed shortly after linking it here, but officially numpy still does not support python 3.13
• and probably more

If py3.13 testbank is green:

• add to general pytest workflow file (runs on every PR and merge)
• remove dedicated py313 workflow file (or maybe keep since it is prerelease)
• add py3.13 to supported versions in pyproject.toml
• updated readme/installation/contributing docs