Incorrect Overflow Casting String to Timestamp

[tustvold]

Describe the bug

When casting strings to timestamps, they are converted to nanoseconds using string_to_timestamp_nanos. This results in erroneous overflow when handling quantities that can't be represented in an i64 as nanoseconds, but can be encoded as a larger timeunit.

To Reproduce

#[test]
fn test_cast_string_to_timestamp_overflow() {
    // let array = TimestampSecondArray::from(vec![chrono::DateTime::MAX_UTC]);
    // let array = cast(&array, &DataType::Utf8).unwrap();

    let array = StringArray::from(vec!["9800-09-08T12:00:00.123456789"]);
    let result = cast(&array, &DataType::Timestamp(TimeUnit::Second, None)).unwrap();
    let result = result.as_primitive::<TimestampSecondType>();
    assert_eq!(result.values(), &[247112596800]);
}

Expected behavior

Additional context

[tustvold]

label_issue.py automatically added labels {'arrow'} from #4034