Function spill_column 

fn spill_column<C: Columnar>(
    column: Column<C>,
    pool: &Pool,
    len_bytes: usize,
    hints: ChunkHints,
) -> ChunkHandle

Serialize a column into a pool slot. The Align variant is already the serialized form and copies in directly. Other variants write their ContainerBytes encoding through a cursor over the slot memory. Sizing is exact, so a short or overlong write is a contract violation and panics.