join, od: report a hyphen-leading value instead of rejecting it

[arbelonson-source]

GNU hands the argument after an option to that option even when it begins with a hyphen, and then reports it as invalid. join and od refused it as an unknown option instead.

Command	GNU	uutils before
join -1 -1 a b	join: invalid field number: '-1'	error: a value is required for '-1 <FIELD>' but none was supplied
join -j -1 a b	join: invalid field number: '-1'	same clap error
od -N -1 a	od: invalid -N argument '-1'	error: unexpected argument '-1' found
od -j -1 a	od: invalid -j argument '-1'	error: unexpected argument '-1' found

The validation that produces GNU's exact wording is already present in both — join -1 abc and od -N abc match GNU byte for byte today. The hyphen-leading value simply never reached it, so this just lets it through with allow_hyphen_values; the existing code then produces the right message unchanged.

Found by differential testing against GNU coreutils 9.11. Follows the same idea as #14256, but those were options where GNU succeeds; these are ones where both fail and only the diagnostic differs, so they are kept separate.

Testing

One regression test per utility, each covering every affected option (-1, -2, -j for join; -N, -j for od). Verified they catch the bug by reverting the two source files alone — both fail, then pass with them restored.

• cargo test --features "join,od" --no-default-features: 116 passed, 0 failed (114 pre-existing, 2 new)
• cargo fmt --check and cargo clippy -p uu_join -p uu_od --all-targets: clean
• 10-case differential check covering the fixed forms plus ordinary ones (od -N 4, od -j 1, join -1 1 -2 1, join -1 abc) as regression cover: all 10 match GNU exactly

Disclosure

Prepared with AI assistance (Claude Code), per the AI policy in CONTRIBUTING.md. On the GPL point raised there: expected behavior was established by running the installed GNU binaries as a black box and recording their output. I did not read GNU coreutils source. All testing above was run locally.

[github-actions]

Binary size comparison:

Individual binary size comparison VS main (threshold: >=5% AND >=4 KB).

Total size of compared binaries: 152.18 MB (+1004 KB, +0.65%)

Significant per-binary changes:
  comm     1.12 MB ->    2.33 MB  (+1.21 MB, +107.29%)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/tail-n0f (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/tail/symlink (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/printf/printf-surprise is now being skipped but was previously passing.