Introduces allocation-free `sum()` and `count_nonzero()` methods for compact integer vectors, extending the `ColumnWeights` trait with `partial_kmer_counts`. Adds parallel partition scanning to the k-mer index for computing per-genome distinct k-mer counts, and exposes a new `--stats` CLI flag to output these statistics as CSV.
Introduce a `stats` module to compute normalized storage efficiency metrics. The new `KmerIndex::bits_per_kmer()` method parallelizes disk I/O across partitions to aggregate file sizes for MPHF, evidence, and matrix components. Publicly export `IndexBitsPerKmer` and add a `--bits-per-kmer` CLI flag to trigger the diagnostic routine and print detailed statistics.
Eric Coissac