Upgrade package and CI support to Django 5.0–5.2

[Copilot]

This PR moves the project from Django 4.2-only support to Django 5.x and aligns metadata/CI with the incremental 5.0 → 5.1 → 5.2 upgrade path in the issue. Existing code paths required no functional changes for 5.x compatibility.

• Packaging metadata

  • Updated runtime dependency in setup.py from django>=4.2,<5.0 to django>=5.0,<5.3.
  • Replaced Django classifier 4.2 with 5.0, 5.1, and 5.2.
  • Dropped Python 3.8/3.9 classifiers to match Django 5 support window.

• CI matrix alignment

  • Updated GitHub Actions test matrix to run:
    • Python 3.10, 3.11, 3.12
    • Django 5.0, 5.1, 5.2
  • This ensures the repository continuously validates the full Django 5.x line requested in the issue.

• Dependency/config delta (example)

  # setup.py
  install_requires = [
      "django>=5.0,<5.3",
  ]