Function list_element_encoded_len 

fn list_element_encoded_len(rows: &Rows, range: Option<Range<usize>>) -> usize

Computes the encoded length for a single list element given its child rows.

This is used by list types (List, LargeList, ListView, LargeListView) to determine the encoded length of a list element. For null elements, returns 1 (null sentinel only). For valid elements, returns 1 + the sum of padded lengths for each child row.