Extract phylogenetic sibling logic into new obikphylo crate

Relocate the `siblings` and `cardcomp` modules from `obikindex` to a dedicated `obikphylo` workspace member. Convert inherent methods on `KmerIndex` into extension traits, update import paths across `obikmer`, and add supporting accessor methods to `obikseq` and `obilayeredmap`. This restructuring reduces the public API surface of `obikindex` while organizing phylogenetic iteration, caching, and distance calculation logic under a dedicated crate.

src/Cargo.lock

@@ -1768,9 +1768,7 @@ dependencies = [
  "obikpartitionner",
  "obikseq",
  "obilayeredmap",
- "obipipeline",
  "obiread",
- "obiskbuilder",
  "obiskio",
  "obisys",
  "obitaxonomy",
@@ -1794,6 +1792,7 @@ dependencies = [
  "obifastwrite",
  "obikindex",
  "obikpartitionner",
+ "obikphylo",
  "obikrope",
  "obikseq",
  "obilayeredmap",
@@ -1843,6 +1842,27 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "obikphylo"
+version = "0.1.0"
+dependencies = [
+ "ndarray",
+ "obicompactvec",
+ "obikindex",
+ "obikpartitionner",
+ "obikseq",
+ "obilayeredmap",
+ "obipipeline",
+ "obiread",
+ "obiskbuilder",
+ "obiskio",
+ "obisys",
+ "rayon",
+ "tempfile",
+ "tracing",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "obikrope"
 version = "0.1.0"