date: fix subfmt-up1, fill-1, pct-pct, and invalid-high-bit-set tests / implement --debug #10940

Performance Regression: -39.09%

❌ 6 regressed benchmarks
✅ 282 untouched benchmarks
⏩ 38 skipped benchmarks¹

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

	Mode	Benchmark	`BASE`	`HEAD`	Efficiency
❌	Simulation	`file_custom_format`	11.7 ms	16 ms	-26.75%
❌	Simulation	`complex_relative_date`	247 µs	258.9 µs	-4.58%
❌	Simulation	`single_date_now`	194.7 µs	207.2 µs	-6.04%
❌	Simulation	`file_tz_abbreviations`	16 ms	24.3 ms	-34.04%
❌	Simulation	`file_iso_dates`	12.3 ms	20.1 ms	-39.09%
❌	Memory	`file_tz_abbreviations`	333.4 KB	529.2 KB	-37%

_{Comparing sylvestre:date-pl-5 (200afd1) with main (e7f2fd9)}

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. ↩