cksum: Use clap's usize parser and default_value("0")

[baa-ableton]

Closes: #11315

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cksum/b2sum. tests/cksum/b2sum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-sha3. tests/cksum/cksum-sha3 is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/cut/bounded-memory (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)
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Note: The gnu test tests/expand/bounded-memory is now being skipped but was previously passing.

[codspeed-hq]

Merging this PR will degrade performance by 5.33%

❌ 13 regressed benchmarks
✅ 289 untouched benchmarks
⏩ 46 skipped benchmarks¹

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	cksum_crc	41.8 KB	44.1 KB	-5.29%
❌	Memory	cksum_sm3	41.7 KB	44 KB	-5.31%
❌	Memory	cksum_blake2b	41.9 KB	44.2 KB	-5.29%
❌	Memory	cksum_md5	41.6 KB	44 KB	-5.32%
❌	Memory	cksum_sysv	41.5 KB	43.8 KB	-5.33%
❌	Memory	cksum_sha256	41.7 KB	44 KB	-5.31%
❌	Memory	cksum_sha224	41.7 KB	44 KB	-5.31%
❌	Memory	cksum_blake3	43.5 KB	45.8 KB	-5.1%
❌	Memory	cksum_sha384	41.8 KB	44.2 KB	-5.29%
❌	Memory	cksum_sha512	41.9 KB	44.2 KB	-5.29%
❌	Memory	cksum_crc32b	41.8 KB	44.1 KB	-5.3%
❌	Memory	cksum_sha1	41.6 KB	44 KB	-5.31%
❌	Memory	cksum_bsd	41.5 KB	43.8 KB	-5.33%

---

_{Comparing baa-ableton:fix/issue-11315 (ec152e4) with main (9397a9c)}

Footnotes

1. 46 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. ↩

[oech3]

Still many Some() are kept.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cksum/b2sum. tests/cksum/b2sum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-sha3. tests/cksum/cksum-sha3 is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/tail/tail-n0f is now being skipped but was previously passing.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cksum/b2sum. tests/cksum/b2sum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-sha3. tests/cksum/cksum-sha3 is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/date/date-locale-hour (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)
Note: The gnu test tests/expand/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cksum/b2sum. tests/cksum/b2sum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-sha3. tests/cksum/cksum-sha3 is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes 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/tty/tty-eof (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/env/env-signal-handler was skipped on 'main' but is now failing.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cksum/b2sum. tests/cksum/b2sum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-sha3. tests/cksum/cksum-sha3 is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/inotify-dir-recreate (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/cut/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.
Congrats! The gnu test tests/dd/no-allocate is now passing!

[baa-ableton]

@oech3

Hey i think we can do another review. I'm a bit new to this so I could use a rather verbose review.

Just wanna touch on the Some()s:
maybe_sanitize_length return signature changed and now returns a UResult with no wrapping needed inside. The remaining Some() at the call sites of checksum_main is structural and unavoidable — checksum_main is shared with utilities that have no --length concept at all and genuinely pass None.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cksum/b2sum. tests/cksum/b2sum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum. tests/cksum/cksum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-a. tests/cksum/cksum-a is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-base64. tests/cksum/cksum-base64 is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-base64-untagged. tests/cksum/cksum-base64-untagged is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-c. tests/cksum/cksum-c is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-raw. tests/cksum/cksum-raw is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-sha3. tests/cksum/cksum-sha3 is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/sm3sum. tests/cksum/sm3sum is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/rm/isatty (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/date/resolution (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Note: The gnu test tests/seq/seq-epipe is now being skipped but was previously passing.

[oech3]

Is checksum_main(algo, 0, matches, format) not enough?

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/cksum/b2sum. tests/cksum/b2sum is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/cksum/cksum-sha3. tests/cksum/cksum-sha3 is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/symlink (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)

[oech3]

Strange... It increased RAM usage even Some() was removed.

[RenjiSann]

Doing this breaks GNU compatibility wrt error printing when the parsing of --length fails.

I am neither for or against doing so. I can hear that our GNU compatibility goal ends at error messages' formatting.
@sylvestre what's our stance here ?

In the current state, this PR both reduces performances (even so slightly) and reduces GNU compatibility, so I'm not particularly favorable to merge it.