feat: support casting strings to durations

[miguelcorderopamphile]

Fixes #4555.

The cast kernels supported strings to intervals, but not to durations. This adds casts from Utf8, LargeUtf8 and Utf8View to Duration in all four units, reusing the existing Parser implementations for the Duration*Types (the same integer parsing the JSON reader uses, #6683).

• can_cast_types accepts the string → duration combination
• dispatch arms added for parse_string (Utf8/LargeUtf8) and parse_string_view (Utf8View)
• tests: safe cast with nulls and invalid values, unsafe error message, large/view variants

cargo test -p arrow-cast --lib: 368 passed.

[Jefffrey]

do we support only casting from numeric values? no units such as 1 hour 10 minutes?

[miguelcorderopamphile]

Currently numeric only: the cast reuses the existing Duration*Type parser impls (the same integer parsing the JSON reader uses).

I can extend it to unit strings like 1 hour 10 minutes by going through the existing string→interval parser and the Interval(MonthDayNano) → Duration cast, which keeps the current semantics (months/days are not convertible — cast_month_day_nano_to_duration nulls/errors them).

I could add it in this PR or keep this one numeric-only — your call.

[Jefffrey]

it would be more useful if we could parse units

[miguelcorderopamphile]

Done in ffa5e92 — non-integer strings now fall back to the interval parser, so "1 hour 10 minutes" casts to any Duration unit. Integer strings behave as before.

Months/days stay non-convertible to match the interval → duration cast (null when safe, error otherwise). I can change that if you'd rather treat "1 day" as 24h.

[Jefffrey]

a good rule of thumb is to be able to roundtrip through the display representation:

arrow-rs/arrow-cast/src/display.rs

Lines 1591 to 1613 in 6db2d4f

	let array = DurationSecondArray::from(vec![
	1,
	-1,
	1000,
	-1000,
	45 * 60 * 60 * 24 + 14 * 60 * 60 + 2 * 60 + 34,
	-45 * 60 * 60 * 24 - 14 * 60 * 60 - 2 * 60 - 34,
	]);
	let iso = format_array(&array, &iso_fmt);
	let pretty = format_array(&array, &pretty_fmt);
	assert_eq!(iso[0], "PT1S");
	assert_eq!(pretty[0], "0 days 0 hours 0 mins 1 secs");
	assert_eq!(iso[1], "-PT1S");
	assert_eq!(pretty[1], "0 days 0 hours 0 mins -1 secs");
	assert_eq!(iso[2], "PT1000S");
	assert_eq!(pretty[2], "0 days 0 hours 16 mins 40 secs");
	assert_eq!(iso[3], "-PT1000S");
	assert_eq!(pretty[3], "0 days 0 hours -16 mins -40 secs");
	assert_eq!(iso[4], "PT3938554S");
	assert_eq!(pretty[4], "45 days 14 hours 2 mins 34 secs");
	assert_eq!(iso[5], "-PT3938554S");
	assert_eq!(pretty[5], "-45 days -14 hours -2 mins -34 secs");

can see how we display days here, so it would make sense to support parsing days

[miguelcorderopamphile]

Done in d047bf0 — days now convert at 24h/day (weeks fold into days in the parser), so pretty display strings roundtrip: "45 days 14 hours 2 mins 34 secs" → 3938554s for Duration(s). Months stay non-convertible since the duration display never emits them.