Imports

Section 18.1 - B-tree running time (legacy compatibility path)

Third-edition-numbered compatibility path for this B-tree development. The canonical fourth-edition source is CLRSLean.FourthEdition.Chapter_18.Section_18_1_B_Tree_Model.RunningTime; this module forwards to it so legacy imports keep working during the compatibility period (see docs/migrations/clrs4.md).