du: match GNU's error for a bad --time value, fix --time-style's help hint

[arbelonson-source]

What

--time validates its value with a plain ShortcutValueParser, so an
unrecognized or ambiguous value produces clap's own generic wording
instead of GNU's grouped-alias wording:

$ du --time=bogus /tmp

# GNU
du: invalid argument 'bogus' for '--time'
Valid arguments are:
  - 'atime', 'access', 'use'
  - 'ctime', 'status'
Try 'du --help' for more information.

# uutils, before this PR
error: invalid value 'bogus' for '--time[=<WORD>...]'

  [possible values: atime, ctime, creation]

For more information, try '--help'.

Fix

Resolve the value against the option's own alias groups by hand,
accepting any unambiguous abbreviation the way GNU does -- including
one that's ambiguous only between aliases of the same choice (e.g.
--time=a unambiguously means atime/access/use) -- and report
GNU's wording, extended with one more group for this implementation's
own creation/birth choice, which GNU's --time does not support
at all. Since that's a real extra choice this implementation accepts,
--time=c is genuinely ambiguous here (between ctime and
creation) even though it isn't in GNU.

Same fix already shipped for wc --total, date --iso-8601/--rfc-3339,
sort --parallel, and uniq --group/--all-repeated (#14293, #14303,
#14304, #14305).

Also fixed

An unrelated but adjacent bug in the same error family: --time-style's
own invalid-argument message already had GNU's wording, but its "Try
... for more information" hint used uucore::execution_phrase() (just
the invoked binary, e.g. target/debug/du) without appending
--help, and quoted full-iso/long-iso/iso where GNU does not:

# GNU
du: invalid argument 'bogus' for 'time style'
Valid arguments are:
  - full-iso
  - long-iso
  - iso
  - +FORMAT (e.g., +%H:%M) for a 'date'-style format
Try 'du --help' for more information.

# uutils, before this PR
du: invalid argument 'bogus' for 'time style'
Valid arguments are:
  - 'full-iso'
  - 'long-iso'
  - 'iso'
  - +FORMAT (e.g., +%H:%M) for a 'date'-style format
Try 'target/debug/du' for more information.

Testing

• cargo test -p uu_du / full tests/by-util/test_du.rs suite: 122 passed, 0 failed.
• Added 3 regression tests: an invalid --time value, an ambiguous one (c), and the fixed --time-style hint.
• Manually diffed every --time value (all real GNU choices/aliases, creation/birth, invalid, ambiguous, empty) against GNU du 9.11 under LC_ALL=C.
• cargo clippy -p uu_du --all-targets -- -D warnings and cargo fmt --check: clean.

---

This PR was written with AI assistance (Claude Opus 5, via Claude Code). I've tested the changes but please review the code carefully.

[oech3]

see #14308 (comment)

[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?
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/follow-name (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/cp/cp-a-selinux 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/misc/close-stdout 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/tail/pipe-f is now being skipped but was previously passing.
Note: The gnu test tests/dd/fail-ftruncate-fstat was skipped on 'main' but is now failing.