Section 21.2 - Linked-list representation (legacy compatibility path)
Third-edition-numbered compatibility path for the linked-list
representation of disjoint sets. The canonical fourth-edition source is
CLRSLean.FourthEdition.Chapter_19.Section_19_2_Linked_List_Representation;
this module forwards to it so legacy imports keep working during the
compatibility period (see docs/migrations/clrs4.md).