Backport all patches to current git, incl. Python 3.12 fixes
    
    This backports all patches to current git head, plus PR #310 to
    allow image size specification in any SI or IEC unit (which we
    need to get an exactly-16GB Workstation disk image). The patches
    are pretty much all to fix issues we ran into with Fedora
    composes anyhow, plus PR #311 to fix compatibility with Python
    3.12 and fix the test suite and PR #312 to fix the test suite
    when running in mock.
    
    We also start actually running the test suite in the package
    build.