panic: repeat string array path overflows capacity calculation

[Dandandan]

Describe the bug

The array execution path for repeat(string, count) can panic on a large count because it multiplies string length by count before checking for overflow.

To Reproduce

SELECT repeat(x, 9223372036854775807)
FROM (VALUES ('abc')) AS t(x);

Actual behavior

thread 'main' panicked at datafusion/functions/src/string/repeat.rs:237:41:
attempt to multiply with overflow

Expected behavior

Return a string-size overflow error, as the scalar path already does, rather than panicking.

Notes

This reproducer uses a one-row input column so it reaches the array path without trying to allocate the full result.