uucore: keep the usage hint when a caret replaced the message

[sylvestre]

A quieted UUsageError became a bare ExitCode, whose usage() is false, so
stdbuf and cut printed "Try '... --help'" on a pipe but not on a terminal.

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[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/retry (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails 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/pr/bounded-memory (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)
Note: The gnu test tests/tail/tail-n0f is now being skipped but was previously passing.

[codspeed-hq]

Merging this PR will degrade performance by 3.78%

⚠️ 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

⚡ 2 improved benchmarks
❌ 4 regressed benchmarks
✅ 351 untouched benchmarks
⏩ 50 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_precision	346.4 ms	403.4 ms	-14.14%
❌	Simulation	numfmt_stream_to_si	414.1 ms	445.1 ms	-6.98%
❌	Simulation	numfmt_to_si_precision[10000]	92 ms	97.3 ms	-5.42%
❌	Simulation	numfmt_large_numbers_si[10000]	96.7 ms	99.9 ms	-3.12%
⚡	Simulation	ls_recursive_deep_tree[(200, 2)]	3.7 ms	3.6 ms	+4.38%
⚡	Simulation	cksum_crc32b	42.4 ms	40.8 ms	+3.92%

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-usage-hint (51b1818) with main (b2a617e)²}

Footnotes

1. 50 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-join (a80036b) during the generation of this report, so main (b2a617e) was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

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