Fix axis ordering in read_region/write_region

[simonrw]

Summary

• create_image and fetch_hdu_info reverse dimensions to present them in C row-major order, but read_region and write_region were passing ranges directly to CFITSIO without reversing
• This caused the ranges to be interpreted with swapped axes, making region operations inconsistent with the rest of the API
• Updated test assertions to match the corrected axis ordering

Test plan

• All 150 existing tests pass with corrected assertions
• Verify read_region/write_region now use consistent row-major axis ordering with create_image/fetch_hdu_info

🤖 Generated with Claude Code

[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request adjusts how image region reading and writing operations interpret user-provided ranges to align with CFITSIO's Fortran column-major convention. User-provided ranges are specified in C row-major order [rows, columns], but the implementation now reverses the iteration order to correctly handle the underlying column-major data layout. Test expectations and comments are updated accordingly to reflect this coordinate system interpretation change.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: fixing axis ordering in read_region/write_region functions to align with the rest of the API.
Description check	✅ Passed	The description comprehensively explains the issue, its impact on API consistency, and the solution implemented, and is directly related to the changeset.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/axis-ordering-region

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No actionable comments were generated in the recent review. 🎉

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.5%. Comparing base (83b76a5) to head (4ba6af5).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
fitsio/src/fitsfile.rs	94.8% <100.0%> (ø)
fitsio/src/images.rs	96.7% <100.0%> (ø)

... and 2 files with indirect coverage changes

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