Function sparse_vector_struct_fields 

pub fn sparse_vector_struct_fields() -> Fields

The canonical Arrow struct fields for a DataType::SparseVector column: Struct { indices: List<UInt32>, values: List<Float32> }. Two parallel variable-length lists in one struct. Both lists are non-null — an empty sparse vector stores as two empty lists, never null. The write and read sides both route through this one definition so they cannot drift (the same lockstep discipline as the temporal structs above).