KV.PrivateSourcePrivate functions, which might be used by the backends.
include Irmin.Private.S
with type Contents.value = contents
and module Hash = Hash
and module Node.Path = Key
and type Node.Metadata.t = metadata
and type Branch.key = branch
and type Slice.t = slice
and type Repo.t = repo
with type Sync.endpoint = unitPrivate content store.
Private branch store.