numfmt: add --grouping option

[mattsu2020]

Summary

• Add --grouping option to numfmt
• Apply locale-specific grouping separators in output
• Enforce conflicts between grouping and --to / --format
• Add regression tests for grouping behavior

[codspeed-hq]

Merging this PR will degrade performance by 9.11%

❌ 9 regressed benchmarks
✅ 279 untouched benchmarks
⏩ 38 skipped benchmarks¹

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	numfmt_round_modes[("up", 10000)]	36.1 ms	39 ms	-7.52%
❌	Simulation	numfmt_padding[(10000, 50)]	51.3 ms	53.4 ms	-3.82%
❌	Simulation	numfmt_round_modes[("down", 10000)]	36.3 ms	39 ms	-7.08%
❌	Simulation	numfmt_round_modes[("towards-zero", 10000)]	36.2 ms	38.9 ms	-6.94%
❌	Simulation	numfmt_large_numbers_si[10000]	38.1 ms	41.5 ms	-8.07%
❌	Simulation	numfmt_to_si_precision[10000]	37.2 ms	40.2 ms	-7.36%
❌	Simulation	numfmt_to_iec[10000]	35.4 ms	38.4 ms	-7.74%
❌	Simulation	numfmt_to_si[10000]	35.3 ms	38.4 ms	-7.98%
❌	Simulation	numfmt_from_si[10000]	33.9 ms	37.3 ms	-9.11%

---

_{Comparing mattsu2020:numfmt-grouping-only (ae1d7de) with main (289d701)}

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. ↩

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/shuf/shuf-reservoir (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/sort/sort-stale-thread-mem (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/shuf/shuf-reservoir (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/sort/sort-stale-thread-mem (fails in this run but passes in the 'main' branch)

[sylvestre]

the unsafe is way too big

please give your to AI the guidance to avoid duplication of code ;)

we probably have what we need in src/uucore/src/lib/features/i18n/decimal.rs already

[mattsu2020]

fix

[sylvestre]

please tell your AI to avoid duplication of code and make it smaller

[sylvestre]

Merge issue

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/usage_vs_getopt (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)

[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?

[sylvestre]

sorry - many jobs have been failing

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/cut/bounded-memory is no longer failing!
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cut/bounded-memory is no longer failing!
Note: The gnu test tests/basenc/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.