Verifies that the pieces of a gs_dist() object are consistent at a
parameter value: names and bounds, finite and vectorized log density,
density integrating to one, quantile inverting cdf, cdf matching the
density, random matching cdf (Kolmogorov-Smirnov), moment conditions
(max_power above default_delta, mean and aparch_moment against
numerical integration). It stops with an error naming the failing field.