test: add rows_read accounting and silent-failure regression tests

[Coding-Dev-Tools]

Summary

Add regression tests for ConversionResult.rows_read accounting and silent-failure detection.

Changes

• tests/test_rows_read_accounting.py: Tests that convert() properly populates rows_read and that conversions which read rows but wrote none are not reported as success.

Testing

CI will run test/coverage/security jobs on this branch.

[github-actions]

🤖 Automated Code Review

✅ Ruff Lint — No issues

⚠️ Ruff Format — Formatting needed

Would reformat: conftest.py
Would reformat: src/datamorph/cli.py
Would reformat: src/datamorph/converters.py
Would reformat: tests/test_cli_error_paths.py
Would reformat: tests/test_converters.py
Would reformat: tests/test_edge_cases.py
Would reformat: tests/test_validate.py
7 files would be reformatted, 3 files already formatted

✅ Secret Detection — Clean

✅ Large Files — Within limits

📊 Diff Stats — 2 file(s) changed

 src/datamorph/converters.py        |  26 +++++++-
 tests/test_rows_read_accounting.py | 126 +++++++++++++++++++++++++++++++++++++
 2 files changed, 150 insertions(+), 2 deletions(-)

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Verdict: ⚠️ Warnings — Lint/format issues found. Recommend fixing before merge.

Automated by Coding-Dev-Tools/.github reusable workflow.

[Coding-Dev-Tools]

[Blocked — failing tests] The 4 new tests in tests/test_rows_read_accounting.py fail against the current converter — result.rows_read is 0 where the tests expect the input row count (assert 0 == 2), and the silent-failure detection test doesn't trip. These are valuable regression tests for the silent-failure class, but they need the accompanying rows_read accounting implemented in the conversion path first. Ran locally: 4 failed, 131 passed. Not merging until the implementation lands and the suite is green.