Function find_longest_length 

fn find_longest_length(
    list_arrays: &[ArrayRef],
    options: &UnnestOptions,
) -> Result<ArrayRef>

Find the longest list length among the given list arrays for each row.

For example if we have the following two list arrays:

l1: [1, 2, 3], null, [], [3]
l2: [4,5], [], null, [6, 7]

If preserve_nulls is false, the longest length array will be:

longest_length: [3, 0, 0, 2]

whereas if preserve_nulls is true, the longest length array will be:

longest_length: [3, 1, 1, 2]