feat(bitvec): add partial Jaccard, fix padding, optimize constructor

Introduces `partial_jaccard_dist` to return raw intersection and union counts, improving Jaccard distance flexibility. Corrects `not()` to explicitly zero padding bits in the final word, ensuring accurate bit-counting for partially-filled words. Adds an optimized `build_from_counts` constructor.

mkdocs.yml

@@ -49,6 +49,7 @@ nav:
       - PersistentBitVec: implementation/persistent_bit_vec.md
   - Architecture:
       - Sequences: architecture/sequences/invariant.md
+      - Kmer index: architecture/index_architecture.md
 
 watch:
   - docmd