Imports

Section 21.4 - Costed union-find execution (legacy compatibility path)

Third-edition-numbered compatibility path for the costed union-find execution. The canonical fourth-edition source is CLRSLean.FourthEdition.Chapter_19.Section_19_4_Analysis.CostedExecution; this module forwards to it so legacy imports keep working during the compatibility period (see docs/migrations/clrs4.md).