base32/base64/basenc: accept a -w value starting with - to match GNU

[AlejandroCoronadoN]

base64 -w -5 (and any -w value that starts with -, e.g. -w -d) was rejected by the argument parser with unexpected argument '-5' found, while GNU takes the token after -w as the wrap size and reports invalid wrap size:

$ printf abc | base64 -w -5
error: unexpected argument '-5' found
$ printf abc | gbase64 -w -5
gbase64: invalid wrap size: '-5'

Adding allow_hyphen_values(true) to the -w/--wrap argument lets the value reach the existing wrap-size parser, which already emits the GNU-matching message. Verified against GNU for -w -5, -w -d, -w -x (all invalid wrap size), with valid values (-w 5, -w0, --wrap=5) and decoding unchanged. The shared base_common.rs covers base32, base64 and basenc.

[codspeed-hq]

Merging this PR will not alter performance

✅ 357 untouched benchmarks
⏩ 50 skipped benchmarks¹

---

_{Comparing AlejandroCoronadoN:base-wrap-hyphen-value (4256338) with main (05a2eee)}

Footnotes

1. 50 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:

GNU test failed: tests/dd/misc. tests/dd/misc is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/df/over-mount-device. tests/df/over-mount-device is passing on 'main'. Maybe you have to rebase?
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/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cat/splice is no longer failing!
Congrats! The gnu test tests/cut/cut is no longer failing!
Congrats! The gnu test tests/cut/mb-non-utf8 is no longer failing!
Congrats! The gnu test tests/dd/partial-write is no longer failing!
Congrats! The gnu test tests/expand/mb is no longer failing!
Congrats! The gnu test tests/ls/stat-free-symlinks is no longer failing!
Congrats! The gnu test tests/mktemp/write-error is no longer failing!
Congrats! The gnu test tests/mv/dir2dir is no longer failing!
Congrats! The gnu test tests/mv/mv-exchange is no longer failing!
Congrats! The gnu test tests/nl/multibyte is no longer failing!
Congrats! The gnu test tests/od/od-float is no longer failing!
Congrats! The gnu test tests/od/od-j is no longer failing!
Congrats! The gnu test tests/ptx/ptx-overrun is no longer failing!
Congrats! The gnu test tests/sort/sort-merge-fdlimit is no longer failing!
Congrats! The gnu test tests/unexpand/mb is no longer failing!
Note: The gnu test tests/dd/fail-ftruncate-fstat was skipped on 'main' but is now failing.