The Modified Half-Normal Distribution // Provides density, distribution, quantile, and random generation functions for the Modified Half-Normal (MHN) distribution, along with moments, mode, and the Fox-Wright Psi function used as the normalizing constant. The MHN distribution arises as a conditional posterior in Bayesian MCMC and generalizes the half-normal, truncated normal, and square-root gamma distributions. Implements efficient sampling via the Sun, Kong Pal (2023) doi:10.1080/03610926.2021.1934700 algorithms and the Gao Wang (2025) doi:10.1080/03610918.2025.2524551 RTDR method.