cksum: small improvements, l10n

[RenjiSann]

This MR brings a few changes to simplify and optimize some parts of the checksum computation

It depends on the #9511 MR

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/cksum/cksum-c is no longer failing!

[codspeed-hq]

CodSpeed Performance Report

Merging #9532 will degrade performances by 16.44%

_{Comparing RenjiSann:cksum-improvements (dc8063d) with main (b2feb82)}

Summary

⚡ 1 improvement
❌ 13 regressions
✅ 112 untouched
⏩ 6 skipped¹

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	b64_decode_ignore_garbage_synthetic	149.4 µs	167 µs	-10.5%
❌	b64_decode_synthetic	149.1 µs	169.1 µs	-11.78%
❌	b64_encode_synthetic	146.2 µs	164.7 µs	-11.25%
❌	cksum_blake3	190.7 µs	207.6 µs	-8.13%
❌	cp_large_file[16]	341.3 µs	361.7 µs	-5.63%
❌	factor_multiple_u64s[2]	178.2 ms	213.3 ms	-16.44%
❌	ls_recursive_wide_tree[(10000, 1000)]	51.3 ms	52.6 ms	-2.46%
❌	mv_force_overwrite	125.2 ms	138.4 ms	-9.51%
❌	mv_single_file	129.7 ms	136 ms	-4.62%
❌	rm_single_file	106.6 ms	119.6 ms	-10.89%
⚡	sort_ascii_c_locale	22.5 ms	21.5 ms	+4.56%
❌	sort_reverse_mixed	38.1 ms	39.1 ms	-2.57%
❌	split_number_chunks	275.5 µs	287.8 µs	-4.27%
❌	wc_bytes_synthetic[500]	164.3 µs	182.9 µs	-10.14%

Footnotes

1. 6 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/tail/overlay-headers (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cksum/cksum-c is no longer failing!

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/cksum/cksum-c is no longer failing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)