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

[sylvestre]

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[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/misc/tty-eof (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)

[codspeed-hq]

Merging this PR will degrade performance by 4.83%

⚠️ 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

❌ 3 regressed benchmarks
✅ 241 untouched benchmarks
⏩ 163 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	numfmt_stream_to_si	414.1 ms	447.2 ms	-7.41%
❌	Simulation	numfmt_stream_to_si_precision	346.4 ms	360.5 ms	-3.92%
❌	Simulation	numfmt_large_numbers_si[10000]	96.7 ms	99.9 ms	-3.12%

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 (b886beb) with caret-od (5a80993)}

Footnotes

1. 163 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. ↩

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