sort: write empty file when input is empty

[hideyosh1]

• adds implementations for this behavior in both threaded and wasi

• adds test for this behavior

Closes #11958

sorry, this is my first contribution, be gentle please...

[chadbrewbaker]

Does this even compile? "chunk" is being used before the definition a few lines later.

[oech3]

Or can we merge ReadResult::EmptyInput => { logic to another => for simplicity?

[hideyosh1]

how so ? just creating a new chunk and passing ReadResult::SortedSingleChunk(first_chunk) ?
but this seems very unwieldy and slow

[chadbrewbaker]

Something like this might avoid a heap allocation? Not sure it matters.

ReadResult::EmptyInput => {
    print_sorted(std::iter::empty::<&[u8]>(), settings, output)?;
}

[hideyosh1]

thanks for your review, i think ive fixed these issues... instead i used
iter::empty(); this is fine?

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/tail-n0f (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/rm/many-dir-entries-vs-OOM is now passing!

[codspeed-hq]

Merging this PR will not alter performance

✅ 11 untouched benchmarks
⏩ 345 skipped benchmarks¹

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_{Comparing hideyosh1:main (6426bc7) with main (17f1777)}

Footnotes

1. 345 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. ↩