df: add tracing zero and rounding

[bakanovskii]

Fixes: #8683
Fixes: #8690

[codspeed-hq]

CodSpeed Performance Report

Merging #8685 will not alter performance

_{Comparing bakanovskii:df-fix-tracing-zero (146ac84) with main (5c15d79)}

Summary

✅ 41 untouched
⏩ 64 skipped¹

Footnotes

1. 64 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. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[sylvestre]

could you please add tests? thanks

[bakanovskii]

could you please add tests? thanks

I refactored the tests to cover both modes or should I add a separate test just for mode with tracing zeroes?

[sylvestre]

yeah, please add a test in tests/by-util/test_df.rs too

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/overlay-headers. tests/tail/overlay-headers is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/misc/stdbuf (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[bakanovskii]

yeah, please add a test in tests/by-util/test_df.rs too

done, however there are some stdbuf error in the CI, is this ok?

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)