Bug: `uu-nl` rejects repeated `-b*` flags that GNU `nl` accepts

[Nyovelt]

Summary

• Tool under test: uu-nl (uutils coreutils) 0.3.0 @ 514291d
• Reference: GNU nl 9.4
• Impact: uu-nl exits with status 1 and prints an error when -b is provided multiple times (e.g. -ba -bt), while GNU nl treats the later flag as overriding the earlier one and succeeds.
• Reproducer (no input files needed):

  printf 'one\ntwo\n' | /usr/local/bin/uu-nl -ba -bt

  (built inside fuzz-utils:latest, Ubuntu 24.04 base)

Expected Result (GNU nl)

$ printf 'one\ntwo\n' | /usr/bin/nl -ba -bt
     1  one
     2  two
$ echo $?
0

Actual Result (uu-nl)

$ printf 'one\ntwo\n' | /usr/local/bin/uu-nl -ba -bt
error: the argument '--body-numbering <STYLE>' cannot be used multiple times

$ echo $?
1

[naoNao89]

coreutils/src/uu/nl/src/nl.rs

Lines 261 to 268 in 975e18c

	.arg(
	Arg::new(options::BODY_NUMBERING)
	.short('b')
	.long(options::BODY_NUMBERING)
	.help(translate!("nl-help-body-numbering"))
	.value_name("STYLE"),
	)
	.arg(

Missing: .action(ArgAction::Append) or similar

• Clap 4.x rejects multiple occurrences by default
• No configuration allows multiple values
• Error occurs at parse time, before application logic