HM Treasury Green Book Cost-Benefit Analysis Primitives // Implements cost-benefit analysis primitives from HM Treasury Green Book guidance (HM Treasury, 2022, 2026): the kinked Social Time Preference Rate ('STPR'), discount factors, net present value ('NPV'), equivalent annual cost, and real-terms rebasing using the GDP deflator. Designed for UK central government appraisal and evaluation. Bundled parameter tables carry vintage metadata for reproducibility.