date: fix handling of case-change flags in locale format specifiers

[CrazyRoka]

Previously, applying flags like '^' (uppercase) or '#' (swap case) to locale-dependent specifiers (like %c, %x, %X) failed to affect the output. This occurred because the implementation passed these specifiers directly to the underlying formatter, which treats %c as a single unit without inheriting flags for its expanded components.

For example, LC_ALL=C TZ=UTC cargo run --bin coreutils date -d 2024-01-01 +%^c produced "2024 M01 1, Mon 00:00:00", whereas GNU date produces "MON JAN 1 00:00:00 2024".

This change pre-processes the format string to expand %c, %x, and %X using nl_langinfo.

This aligns behavior with GNU coreutils and we are now passing subfmt-up1 edge case in tests/date/date.pl

[github-actions]

GNU testsuite comparison:

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

[sylvestre]

lot of jobs are failing

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/id/smack was skipped on 'main' but is now failing.
Note: The gnu test tests/mkdir/smack-no-root was skipped on 'main' but is now failing.
Note: The gnu test tests/mkdir/smack-root was skipped on 'main' but is now failing.

[github-actions]

GNU testsuite comparison:

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

[ChrisDryden]

Didn't realize there was already a PR for this when I was investigating the date gnu tests failures here: #10242

I ended up making a PR to Jiff to add support for these modifiers: BurntSushi/jiff#488

These are pre-made configs actually so theres nothing stopping us from making our own custom Config that has support for all of the modifiers and this way

[sylvestre]

@CrazyRoka sorry, could you please rebase it ?
it looks good now

[codspeed-hq]

Merging this PR will degrade performance by 3.91%

❌ 1 regressed benchmark
✅ 281 untouched benchmarks
⏩ 38 skipped benchmarks¹

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	cp_large_file[16]	115.2 KB	119.9 KB	-3.91%

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_{Comparing CrazyRoka:date-implement-locale-specific (f3ab2c5) with main (d72d6f7)}

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/tty/tty-eof (passes in this run but fails in the 'main' branch)