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/obikpartitionner/src/index_layer.rs

@@ -5,7 +5,7 @@ use cacheline_ef::{CachelineEf, CachelineEfVec};
 use epserde::prelude::*;
 use obicompactvec::{PersistentCompactIntMatrix, PersistentCompactIntVec};
 use obidebruinj::GraphDeBruijn;
-use obilayeredmap::{OLMError, layer::Layer};
+use obilayeredmap::{EvidenceKind, OLMError, layer::Layer};
 use obilayeredmap::meta::PartitionMeta;
 use obiskio::{SKError, SKFileMeta, SKFileReader};
 use ptr_hash::{PtrHash, bucket_fn::CubicEps, hash::Xx64};
@@ -44,6 +44,7 @@ impl KmerPartition {
         min_ab: u32,
         max_ab: Option<u32>,
         with_counts: bool,
+        evidence: &EvidenceKind,
     ) -> Result<usize, SKError> {
         let part_dir = self.part_dir(i);
         let dedup_path = part_dir.join("dereplicated.skmer.zst");
@@ -119,6 +120,12 @@ impl KmerPartition {
             Layer::<()>::build(&layer_dir).map_err(olm_to_sk)?;
         }
 
+        // For approximate evidence: replace the exact evidence bundle with a
+        // fingerprint.  For exact evidence, build() already wrote it.
+        if let EvidenceKind::Approx { b, z } = evidence {
+            Layer::<()>::build_approx_evidence(&layer_dir, *b, *z).map_err(olm_to_sk)?;
+        }
+
         // Write meta.json in the index/ directory so LayeredMap::open works
         // (e.g. for subsequent merge operations).
         let index_dir = layer_dir.parent().expect("layer_dir has a parent");