python 3.12, setuptools and venv

[elikoga]

Since python/cpython#95299 we need to ensure we have a setuptools ourselves.
They changed pip freeze behaviour in python 3.12 too: pypa/pip#12032

This leaves us with 2 options:

1. We could lock all dependencies with pip freeze --all but:
   • this would also lock pip, wheel to a specific version, which is a change in behaviour
   • we would need to update the requirements.lock to update the version of pip used
2. We could forbid projects with mixed python >= 3.12 and < 3.12 versions in their appenv-python-preference list
   • this would prevent the issue from happening in the first place
   • we would need to inform users about this change

To understand the second option better, it is important to know that batou only uses the first python version in the appenv-python-preference list that is actually installed on the system.

This means that if you have 3.12,3.11 as your appenv-python-preference and 3.12 is installed, batou will use 3.11 for lockfile preparation and 3.12 for venv creation. The resulting lockfile will not contain setuptools and pip freeze will not show setuptools either. This lockfile is incompatible with python 3.12, and once a user without 3.12 installed tries to create a venv, they will run into the issue described above.

Also, if you have 3.12,3.11 as your appenv-python-preference and 3.11 is installed, batou will use 3.11 for lockfile preparation and 3.11 for venv creation. The resulting lockfile will not contain setuptools and pip freeze will not show setuptools either. This does not immediately cause an issue, but once a user with 3.12 installed tries to create a venv, they will run into the issue described above.

This PR does pip freeze --all --exclude pip if both python >= 3.12 and < 3.12 are in the appenv-python-preference list. This mimics the behaviour of pip freeze after the change in python 3.12.

[elikoga]

~~Hm this doesn't look good. It seems like the appenv environment depends on the executing python version due to the unconditional pip install pip --upgrade.

With newer python versions, creating a new venv doesn't include setuptools anymore, but batou requires setuptools and complains.~~

The correct choice is not to modify the pip freeze call, but instead install setuptools

[elikoga]

Ah, I know what we need: #1

The update command needs to migrate the project for 3.12 by reinstalling the required packages and updating the lockfile based on that. In the end, the new lockfiles include an explicit setuptools dependency. The upgrade path is also handled and no erroneous project state is introduced