Section 21.1 - Disjoint-set operations (legacy compatibility path)
Third-edition-numbered compatibility path for the disjoint-set operations.
The canonical fourth-edition source is
CLRSLean.FourthEdition.Chapter_19.Section_19_1_Disjoint_Set_Operations;
this module forwards to it so legacy imports keep working during the
compatibility period (see docs/migrations/clrs4.md).