fix: return an empty iterator for empty worksheets

[ryanduguid]

Summary

Calling iter_rows() on an empty worksheet raises PanicException because its range has no start coordinate. Default the private coordinate and return exhaustion before updating the counter for an empty range, so repeated next() calls also stay exhausted.

The regression reuses the existing XLSX, XLS, XLSB and ODS fixtures and covers empty iteration, repeated StopIteration and an identity sentinel default.

Verification

• An initial empty-iteration regression fails all four formats on unchanged compiled source with Python 3.12.15; its original suite passes 51 tests with one existing expected failure.
• On Linux with Python 3.12.14, pip install -e . succeeds, pytest passes 55 tests with that same expected failure, and all 14 pre-commit run --all-files hooks pass.
• Six non-empty fixture samples have matching JSON-rendered values and offsets, including sheets starting at (1, 1). Their iterators also work after external workbook/sheet references are gone.
• A temporary module-private Rust test-profile probe passes repeated empty calls at u32::MAX; removing only the empty guard produces an arithmetic overflow. The probe restores the source and is outside this PR.

Risks and unverified checks

This changes empty-range iterator construction and exhaustion. Final Windows/macOS native builds, other Python versions, PyPy, free-threaded Python, PyEmscripten, release wheels, coverage and successful upstream CI remain unverified. The existing unsafe lifetime arrangement has not received a general audit.

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
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• Run ID: b6c29140-d30e-4018-8045-30895b2b5ebc

📥 Commits

Reviewing files that changed from the base of the PR and between 84fa0e4 and f582568.

📒 Files selected for processing (2)

• src/types/sheet.rs
• tests/test_base.py

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📝 Walkthrough

Walkthrough

Empty sheet ranges now initialize without a missing-start panic and stop iteration immediately. Tests cover empty sheets in XLSX, XLS, XLSB, and ODS workbooks.

Changes

Empty Sheet Iteration

Layer / File(s)	Summary
Empty range handling src/types/sheet.rs, tests/test_base.py	from_range defaults a missing range start to (0, 0). __next__ returns None for an empty range. Tests check unset sheet bounds, repeated exhaustion, and next() with a default across four workbook formats.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to f5825

Empty worksheets now yield no rows and remain exhausted on subsequent calls. The reviewed change presents no actionable merge-blocking risk.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: empty worksheets now produce an empty iterator.

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_{A rabbit checks a sheet so wide,
Finds no rows waiting there inside.
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[dimastbk]

Thanks!