Update Python & Django supported versions + migrate to ruff

[samiashi]

This PR updates the project for the current supported Python/Django matrix and folds in the outstanding callback feature from #13 so the maintenance work lands in a single PR.

Summary

• drop support for Python 3.7, 3.8 and 3.9
• keep support on Python 3.10 and add support for Python 3.11, 3.12, 3.13 and 3.14
• drop support for Django < 4.2
• add support for Django 5.0, 5.1, 5.2 and 6.0
• replace flake8 with ruff
• clean up packaging metadata for modern setuptools / wheel builds
• fix auto-import handling for dynamic models registered at runtime
• add ADMIN_SHELL_CALLBACK so projects can audit or log shell executions after each successful run

Notes

The dynamic model fix addresses cases where Django Admin Shell tries to import models that are registered in Django's app registry but are not directly exposed as attributes on their declared module.

The callback support was cherry-picked from #13 and adapted to the current branch. The docs, tests and changelog entry are included here as well, so this PR supersedes #13.

[djk2]

Hi. Sorry for very very long time without any response.
I will review this PR in this week.
Looks very nice. Thank You

[samiashi]

@djk2 Just wanted to ping you and see if we can get this reviewed

[samiashi]

This PR now supersedes #13. I cherry-picked the callback feature here, adapted it to the current branch, and included the docs/tests/changelog updates so the work can merge through a single PR.