leiden(), modularity() and
cluster_libreville() (igraph / bluster interface).find_clusters(): leiden() with the interface of Seurat::FindClusters;
with_libreville() runs code (e.g. CHOIR) with FindClusters replaced by it.neosbm(): exact on graphs with self-loops (Seurat's SNN graphs have a unit
diagonal); the block counts had drifted from the partition's.