Compatibility with Python 3.12, ModuleNotFoundError: No module named 'imp'

Hello,

the imp module was removed from Python 3.12 and it breaks breezy. It would be good to port Breezy to use importlib instead. As a stopgap measure, in Fedora, we are adding a dependency on zombie-imp package.

https://pypi.org/project/zombie-imp/

<mock-chroot> sh-5.2# brz
Traceback (most recent call last):
  File "/usr/bin/brz", line 75, in <module>
    main()
  File "/usr/lib64/python3.12/site-packages/breezy/__main__.py", line 55, in main
    import breezy.commands
  File "/usr/lib64/python3.12/site-packages/breezy/commands.py", line 51, in <module>
    from .plugin import disable_plugins, load_plugins, plugin_name
  File "/usr/lib64/python3.12/site-packages/breezy/plugin.py", line 41, in <module>
    import imp
ModuleNotFoundError: No module named 'imp'