30.2 FFT 3. Exact and Padded Costs (legacy compatibility path)
Third-edition-numbered compatibility path for this module. The canonical
fourth-edition source is
CLRSLean.FourthEdition.Chapter_30.Section_30_2_DFT_And_FFT.RecursiveFFT.Costs;
this module forwards to it so legacy imports keep working during the
compatibility period (see docs/migrations/clrs4.md).