split: flush BufWriter before replacing to detect write errors

[ChrisDryden]

This fixes an issue we have with our buffer writers where we do not flush the buffers before they are dropped which means that if there is an error when writing the buffers it will be suppressed. This change also adds the filename to the struct so that the error message is able to provide the file name to match the gnu implementation.

This should address the test tests/split/split-io-err

[ChrisDryden]

I got a local clippy error for this, then I fixed it and now its failing in the CI? 🤔

[codspeed-hq]

Merging this PR will degrade performance by 67.52%

⚡ 1 improved benchmark
❌ 6 regressed benchmarks
✅ 277 untouched benchmarks
⏩ 38 skipped benchmarks¹

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	split_lines	5.7 ms	6 ms	-4.78%
❌	Simulation	split_bytes	507.8 µs	1,183.5 µs	-57.09%
❌	Simulation	split_numeric_suffix	5.9 ms	6.1 ms	-4.27%
⚡	Memory	split_number_chunks	1,127.9 KB	231.9 KB	×4.9
❌	Memory	split_bytes	46.2 KB	142.4 KB	-67.52%
❌	Memory	split_lines	46.2 KB	140.9 KB	-67.19%
❌	Memory	split_numeric_suffix	78.4 KB	187.2 KB	-58.13%

---

_{Comparing ChrisDryden:fix-split-io-err (9f69014) with main (dec633c)}

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. ↩

[ChrisDryden]

Its now passing the "tests/split/split-io-err" but the comment didn't succeed due to an issue with determining the prior gnu results

[ChrisDryden]

The performance decline can probably be helped with this: #10251

[ChrisDryden]

I'm trying a new approach that combines the two PR's, one that reuses the bufwriter and one that handles the errors correctly, I can split them up but wanted to see if the performance degradation is still there

[ChrisDryden]

Its a bit too much code, going to do the re-usable buffer PR before the GNU test fix PR, but just waiting to see the codspeed results

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/pr/bounded-memory. tests/pr/bounded-memory is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/split/filter. tests/split/filter is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?
Congrats! The gnu test tests/factor/t33 is no longer failing!
Congrats! The gnu test tests/factor/t34 is no longer failing!
Congrats! The gnu test tests/split/split-io-err is no longer failing!
Note: The gnu test tests/basenc/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/printf/printf-surprise is now passing!