Introduce a new `Sparse` format alongside existing `Columnar` and `Packed` variants, enabling optimized row-major pairwise counting for distance and similarity metrics via the `CountPartials` trait. Update storage detection priorities, extend matrix dispatch logic to sparse backends, and correct diagonal/off-diagonal formulas in bit matrix partial computations. Expand layer APIs with format-agnostic `nonzero_iter`, update usage documentation for the `--sparse` flag, and add comprehensive tests verifying roundtrip integrity and metric equivalence against dense implementations.
Introduces raw mapping and iteration APIs that bypass membership checks, clarifies variant-specific storage layouts and auto-detection logic, and documents optimized batch access patterns with caller-provided buffers. Removes the outdated obicompactvector_reflexion.md specification to consolidate architectural details into current implementation docs.
Eric Coissac