test(coverage): reach full Python coverage

[atdr]

What changed

Adds focused tests for the remaining Python edge cases across versioning, airport handling, configuration, importers, models, Passport data preparation, and storage. It also brings scripts/refresh_airline_codes.py into the configured coverage scope and tests its Wikidata transformation, CSV writing, reporting, and entrypoint behavior without network access.

Why

The package had 29 uncovered lines plus partial branches, while the maintainer script was absent from the report entirely. This makes every measured Python statement and branch visible and exercised; browser execution of Passport's authored JavaScript is tracked separately in #62.

Checks

• ./venv/bin/ruff check . and ./venv/bin/ruff format . pass
• ./venv/bin/pytest -q passes
• Docs updated in this PR, if this changes a config option, an importer, or an emissions provider
• Tests added or updated, if this changes behaviour
• Skimmed gh issue list for open issues this change touches

Test plan

Ran pytest -q --cov --cov-report=term-missing --cov-fail-under=100: 412 tests passed, with 1,596 statements and 522 branches at 100% coverage. Ran the complete pre-commit suite, including Ruff, Markdownlint, mdformat, YAML and JSON checks; every hook passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (da28530) to head (95f3683).

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #63      +/-   ##
===========================================
+ Coverage   96.99%   100.00%   +3.00%     
===========================================
  Files          19        20       +1     
  Lines        1499      1596      +97     
  Branches      239       261      +22     
===========================================
+ Hits         1454      1596     +142     
+ Misses         29         0      -29     
+ Partials       16         0      -16     

see 11 files with indirect coverage changes

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