Relocates `SiblingAnnex`, `FamilyMask`, and `SiblingAnnexBuilder` from `obicompactvec` to the local `obikphylo::siblings` module. Replaces the previous implementation with a memory-mapped version using `memmap2`, featuring a 2-byte-per-slot layout, explicit bitfield manipulation, and support for concurrent atomic writes. Updates all sibling module imports to local paths and adds the `memmap2` dependency to `obikphylo`.
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.
Eric Coissac