Add diagnostic logging and minor internal refactoring

Introduce runtime dimension tracking, matrix shape validation, and per-layer diagnostics across multiple modules to improve execution observability. Extract intermediate computation results into local variables, standardize collection patterns in partial methods, and replace naive iteration with optimized pairwise counting. All modifications are strictly additive or structural; public APIs, data models, and core logic remain unchanged.

src/obikindex/src/distance.rs

@@ -121,7 +121,6 @@ impl KmerIndex {
                     )));
                 }
             };
-            tracing::info!("distance matrix final: {}x{}", matrix.shape()[0], matrix.shape()[1]);
 
             let shared = if shared_kmers {
                 let (inter, _) = BitPartials::partial_jaccard(&global);