seq: point the caret at the failing part of a format

[sylvestre]

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[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/tail-n0f (passes in this run but fails in the 'main' branch)

[codspeed-hq]

Merging this PR will degrade performance by 4.79%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 1 regressed benchmark
✅ 56 untouched benchmarks
⏩ 350 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	du_wide_tree[(5000, 500)]	19.1 ms	20.1 ms	-4.79%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing caret-seq (7e3d1f5) with caret-od (7ee143f)²}

Footnotes

1. 350 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on caret-od (f2987b5) during the generation of this report, so 29ff3df was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

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