fold: add -p/--punctuation flag for tiered break-point folding

[abdorah]

As I said in an earlier comment in the issue 13316, I've implemented -p / --punctuation as a standalone flag (no argument). When the line hits the width limit, it searches backwards through
the buffered content for the best break point using this priority: sentence-ending punctuation (. ! ? :) -> clause punctuation (, ;) -> whitespace -> any non-alphanumeric character -> hard cut at width.

The rightmost match of the highest-priority tier wins, which maximizes line usage while still preferring semantically meaningful breaks. This is mutually exclusive with -s (enforced by clap). The tiered fallback means a single -p invocation replaces what would otherwise require piping through fold four times with different break characters.

The character sets are hardcoded to ASCII for now but the structure makes it straightforward to extend with locale-aware or CJK punctuation (e.g., 。 、 ？) in a follow-up if needed.

This has changed many things in the way that fold used to work. Since the only attribute that requires 'back tracking' of spaces is space itself, we only had a true or false switch for that, which is perfectly fine, but for an intelligent fold like the one suggested by Dmole, we need more than that, hence the big changes to the fold context.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ 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

⚡ 4 improved benchmarks
❌ 5 regressed benchmarks
✅ 322 untouched benchmarks
⏩ 46 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	shuf_lines[100000]	27.4 ms	32.2 ms	-14.89%
❌	Simulation	fold_many_lines[100000]	57.3 ms	63.6 ms	-9.85%
❌	Simulation	shuf_repeat_sampling[50000]	4.5 ms	5 ms	-9.83%
❌	Simulation	fold_custom_width[50000]	22.9 ms	25.2 ms	-9.09%
❌	Memory	fold_many_lines[100000]	26.7 KB	27.6 KB	-3.38%
⚡	Simulation	false_consecutive_calls	199.4 ns	170.3 ns	+17.13%
⚡	Simulation	true_consecutive_calls	199.4 ns	170.3 ns	+17.13%
⚡	Simulation	unexpand_large_file[10]	291.9 ms	282.3 ms	+3.41%
⚡	Simulation	unexpand_many_lines[100000]	139.3 ms	134.7 ms	+3.4%

Tip

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

---

_{Comparing abdorah:main (e1eece4) with main (b42827c)}

Footnotes

1. 46 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. ↩

[oech3]

Suggested change

.short('p')

Please don't add short option which potentially conflicts with GNU's new options.