ls: break a tie in the time sort with the name

[luantaraschi]

Every sort in sort_entries falls back on the name when its key ties, apart
from the sort by time. Sort::Size, Sort::Version, Sort::Extension and
Sort::Width all end in a .then(...) on the name; Sort::Time was a bare
sort_unstable_by_key on the timestamp.

Entries sharing a timestamp therefore came out in the order the directory was
read in, and since the sort is unstable that order was not guaranteed either.
Four files created at the same mtime, against GNU coreutils 9.7:

	GNU	before	after
ls -t in LC_ALL=C	Mike alpha bravo zulu	alpha bravo zulu Mike	Mike alpha bravo zulu
ls -t in en_US.UTF-8	alpha bravo Mike zulu	alpha bravo zulu Mike	alpha bravo Mike zulu

alpha bravo zulu Mike is what ls -U prints, so the old output was the raw
directory order.

GNU breaks the tie with the collation rather than with the bytes, which is why
the two locales disagree on where Mike goes. The comparison Sort::Name
already builds is hoisted out of the match so the fallback uses that same one.

Checked against GNU for -t, -tr, -t -u and -t -c in both locales, and
with distinct timestamps to confirm the primary ordering is unchanged.

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[codspeed-hq]

Merging this PR will degrade performance by 4.09%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 2 regressed benchmarks
✅ 355 untouched benchmarks
⏩ 50 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	du_summarize_balanced_tree[(5, 4, 10)]	16.2 ms	16.9 ms	-4.21%
❌	Simulation	ls_recursive_long_all_balanced_tree[(6, 4, 15)]	289.2 ms	301.2 ms	-3.97%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing luantaraschi:fix/ls-time-sort-tiebreak (c7fbfea) with main (df30282)}

Footnotes

1. 50 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. ↩

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[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/inotify-dir-recreate (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/cut/cut-huge-range is now passing!
Skip an intermittent issue tests/pr/bounded-memory (was skipped on 'main', now failing)
Skip an intermittent issue tests/tail/tail-n0f (was skipped on 'main', now failing)