Section 21.3 - Disjoint-set forests (legacy compatibility path)
Third-edition-numbered compatibility path for the disjoint-set forests.
The canonical fourth-edition source is
CLRSLean.FourthEdition.Chapter_19.Section_19_3_Disjoint_Set_Forests;
this module forwards to it so legacy imports keep working during the
compatibility period (see docs/migrations/clrs4.md).