tee: allow multiple -a flags

[sylvestre]

fixes
https://bugs.launchpad.net/ubuntu/+source/rust-coreutils/+bug/2134578

[ChrisDryden]

This would be a good test to upstream to the gnu test suite

[ChrisDryden]

I'm trying to brainstorm how to systemically test to see the variance with multiple flags for all of the options, given how simple the fix is, it would be good to make a script to go through every option and see what happens when multiple of a flag is provided or validate this is a niche use case.

[sylvestre]

probably a variance of fuzz/fuzz_targets/fuzz_non_utf8_paths.rs

[codspeed-hq]

Merging this PR will degrade performance by 27.39%

❌ 7 regressed benchmarks
✅ 275 untouched benchmarks
⏩ 38 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	sort_unique_locale[500000]	33.6 MB	39.8 MB	-15.5%
❌	Memory	sort_ascii_only[500000]	22.2 MB	28.3 MB	-21.77%
❌	Memory	sort_long_line[160000]	712.6 KB	981.4 KB	-27.39%
❌	Memory	sort_mixed_data[500000]	22.9 MB	27.1 MB	-15.71%
❌	Memory	sort_numeric[500000]	75.5 MB	79.2 MB	-4.67%
❌	Memory	sort_accented_data[500000]	22.1 MB	28.3 MB	-21.79%
❌	Memory	sort_key_field[500000]	47.8 MB	51.8 MB	-7.62%

---

_{Comparing sylvestre:tee-a (14c517e) with main (f2bec7b)}

Footnotes

1. 38 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. ↩