Relax Python version pinning

We pin the version of Python to 3.11 so that we can gather the correct labgrid PyPI package.

With the new UV support in rules_python (or rules_uv), we can generate a lock file that is "universal".

This will allow a single generated requirements.txt to be supported for all pip.parse Python versions.

Adding a pip.parse hub for each Python version, we can then do a select on the //labgrid:pkg for the Python interpreter version.

Downstream users can then use any version of Python in their rules_python rules and the correct labgrid package will be resolved.