Improve display of Python versions (#1029)
In https://github.com/astral-sh/puffin/pull/986 there was some confusion
about what these values are set to and I noticed that we never actually
display the target version being used for a resolution.
- Consistently display the Python interpreter being used, i.e. make it
clear that we are referring the the interpreter/installed Python version
and always show the version number
- Display the target Python version during solving
