Function encode_fixed_size_list 

pub fn encode_fixed_size_list(
    data: &mut [u8],
    offsets: &mut [usize],
    rows: &Rows,
    opts: SortOptions,
    array: &FixedSizeListArray,
)

Encodes the provided FixedSizeListArray to out with the provided SortOptions

rows should contain the encoded child elements