cksum, hashsum: Manually error standalone --warn's and comment why

[oech3]

No description provided.

[codspeed-hq]

Merging this PR will degrade performance by 4.25%

Summary

❌ 1 regressed benchmark
✅ 141 untouched benchmarks
⏩ 37 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	cksum_blake3	218.9 µs	228.6 µs	-4.25%

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_{Comparing oech3:warn-bad-workaround (3c821b2) with main (30239e6)}

Footnotes

1. 37 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. ↩

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[oech3]

I can't fix cargo-deny. @RenjiSann

[oech3]

I'm very sad. But it seems this is best method until clap 5 was released...

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)