Update CI and tests

[khaeru]

Various housekeeping changes:

• Adjust code to satisfy mypy with latest version and dependencies.
• Update "pytest" CI workflow:
  • Split the "diagnostics" to a separate job.
  • Add a code quality/pre-commit job.
  • Update third-party actions.
  • Run on all 3 supported operating systems and Python up to 3.12.
• Convert packaging from setup.{cfg,py} to pyproject.toml.
• Use ruff and mypy via pre-commit for code quality checks.
• Adjust for "Turkey" no longer appearing in the ISO 3166 database.
• Xfail certain tests: in particular, those using data via OpenKAPSARC that are no longer available because the provider has removed them.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (c92baa3) 73.12% compared to head (40e254a) 73.20%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #84 +/- ## ========================================== + Coverage 73.12% 73.20% +0.07% ========================================== Files 34 42 +8 Lines 1388 1601 +213 ========================================== + Hits 1015 1172 +157 - Misses 373 429 +56 ```

:umbrella: View full report in Codecov by Sentry.
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