feat: add approximate evidence matching and index estimation CLI

Introduces a new `estimate` CLI subcommand to calculate bloom filter size, evidence bits, and false-positive rates for approximate indexing. Updates the index building and querying pipelines to support both exact and approximate evidence types via a unified `EvidenceKind` abstraction. Refactors `MphfLayer` and partition index builders to route operations based on the selected evidence mode, and adds the required `obilayeredmap` dependency.

src/obikindex/src/index.rs

@@ -144,6 +144,7 @@ impl KmerIndex {
         let n = self.partition.n_partitions();
         let t = Stage::start("index");
         let with_counts = self.meta.config.with_counts;
+        let evidence = self.meta.config.evidence.clone();
         let total_kmers = AtomicUsize::new(0);
 
         let pb = Arc::new(Mutex::new(
@@ -153,7 +154,7 @@ impl KmerIndex {
         ));
 
         (0..n).into_par_iter().for_each(|i| {
-            match self.partition.build_index_layer(i, min_ab, max_ab, with_counts) {
+            match self.partition.build_index_layer(i, min_ab, max_ab, with_counts, &evidence) {
                 Ok(0) => {}
                 Ok(n_kmers) => {
                     total_kmers.fetch_add(n_kmers, Ordering::Relaxed);