tee: match GNU's error for a bad --output-error value

[arbelonson-source]

What

An unrecognized or ambiguous --output-error value produces clap's
own generic wording instead of GNU's:

$ echo hi | tee --output-error=bogus f

# GNU
tee: invalid argument 'bogus' for '--output-error'
Valid arguments are:
  - 'warn'
  - 'warn-nopipe'
  - 'exit'
  - 'exit-nopipe'
Try 'tee --help' for more information.

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

  [possible values: warn, warn-nopipe, exit, exit-nopipe]

For more information, try '--help'.

Fix

Unlike the other options fixed in this same series (#14293, #14303,
#14304, #14305, #14306, #14307), --output-error keeps its
ShortcutValueParser rather than being resolved by hand: each of its
choices carries its own description, rendered as clap's "Possible
values:" block in --help, e.g.:

      --output-error[=<output-error>]
          set write error behavior

          Possible values:
          - warn:        produce warnings for errors writing to any output
          - warn-nopipe: produce warnings for errors that are not pipe errors ...
          ...

That per-choice text only a value_parser can supply to clap's help
renderer, so dropping the parser (as the other fixes in this series
do) would either lose that --help output or require hand-rolling
the same metadata a second time just to feed it back to clap for
display -- not worth it for one option. Instead, this intercepts a
rejection specifically on --output-error right after parsing and
re-reports it with GNU's wording (checking for an exact match first,
since warn and exit are themselves prefixes of warn-nopipe and
exit-nopipe); every other clap error -- unknown flags, --help,
--version, etc. -- still goes through the exact same shared
formatter as before, unchanged.

Testing

• cargo test -p uu_tee / full tests/by-util/test_tee.rs suite: 37 passed, 0 failed.
• Added 2 regression tests: an invalid value and an ambiguous one (wa, between warn and warn-nopipe).
• Manually diffed every --output-error value (all real choices/abbreviations, invalid, ambiguous, empty) against GNU tee 9.11 under LC_ALL=C.
• Manually confirmed --help/-h/--version and unrelated errors (e.g. an unknown flag) are unaffected.
• cargo clippy -p uu_tee --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]

We tries to show error message better than GNU. So clap provided errors itself are not issue about compatibility.
clap has more infomation generally.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/pr/bounded-memory (was skipped on 'main', now failing)