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.
Eric Coissac
b0890d1781