Function merge_file_list 

pub fn merge_file_list<'a, T, V, B, F>(
    views: &'a [V],
    out: &mut B,
    get_list: F,
) -> usize
where
    B: Buffer,
    T: ReadAt<'a>,
    F: Fn(&'a V) -> ListView<'a, T>,

Merge a List(FileBlob) field — identical wire format to List(String): each element is a forward-offset pointer to [len: u32][bytes...]. Reuses the same two-pass block-copy strategy as merge_string_list.

Returns

The slot of the length-prefix u32, or 0 if all views were empty.