Learned-sparse (SPLADE / BGE-M3) vector type for the Uni graph database.
A leaf crate with zero uni-* dependencies — the same layering as
uni-btic. It owns the [SparseVector] type, its validating constructor,
the lossless binary [mod@encode] codec, the pure scoring kernels in
[mod@ops] (notably [ops::sparse_dot]), and [SparseError]. All
glue — Value/DataType variants, Arrow lowering, CV tag framing, DDL,
the index — lives in the integration crates that depend on this one.