cksum: Move --check confliction to clap

[oech3]

ref #9992

error: the argument '--check' cannot be used with '--****'

For more information, try '--help'.

[codspeed-hq]

CodSpeed Performance Report

Merging #10028 will degrade performance by 6.4%

_{Comparing oech3:cksum-clap-bin-txt-c (907a8ab) with main (666c6df)}

Summary

❌ 1 regression
✅ 138 untouched
⏩ 37 skipped¹

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Efficiency
❌	cksum_blake3	210.1 µs	224.5 µs	-6.4%

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:

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