Added a `col_weights` method to index layers for computing per-genome column sums or presence k-mer counts. Refactored `obikstats` to implement the `Algorithm` trait with a two-phase `new`/`run` model, replacing manual layer resolution with `IndexCache` for eager file I/O. Simplified per-genome counting logic and updated public exports and dependencies accordingly.
This commit partitions the obikindex crate into multiple focused subcrates (obikfilter, obikmerge, obikquery, obikrebuild, obikselect, obikstats, obikdump, and obikidxcache) to reduce coupling and clarify module boundaries. It standardizes error handling across the workspace using OKIError and OKIResult, updates index APIs to support lazy, disk-backed partition access, and migrates NUMA system utilities to a new obisys crate. All modifications are structural, focusing on dependency graph expansion, import path updates, and API surface reorganization without altering core runtime behavior.