Revamp tooling

[mostafa]

Changes:

• Migrate requirements.txt and requirements_test.txt to pyproject.toml
• Partially replace poetry with pip
• Use ruff to format and lint/check code
• Reformat code with ruff and ignore refs to not show up in blame
• Migrate pytest.ini and mypy.ini and pyproject.toml and remove residual files
• Remove .flake8
• Remove support for Python 3.9
• Upgrade Django patch versions
• Add support for Django 5.0.x
• Upgrade GitHub Actions
• Update GitHub Actions to use poetry for running commands
• Update README with version compatibility information
• Update dependencies:
  • Closes Bump coverage from 7.2.7 to 7.5.0 #280
  • Closes [Snyk] Security upgrade sqlparse from 0.4.4 to 0.5.0 #276
  • Closes Bump responses from 0.23.3 to 0.25.0 #273
  • Closes Bump pytest from 7.4.0 to 8.1.1 #265
  • Closes Bump flake8 from 5.0.4 to 7.0.0 #262

Part of #285.