Function unary_kernel 

pub fn unary_kernel<T, V, F, Arr>(
    ca: &ChunkedArray<T>,
    op: F,
) -> ChunkedArray<V>
where
    T: PolarsDataType,
    V: PolarsDataType<Array = Arr>,
    Arr: Array,
    F: FnMut(&T::Array) -> Arr,

Applies a kernel that produces Array types.