HyperbolicInverseLangevinDerivative Method

High-accuracy derivative of the inverse Langevin function, d(L^-1)/dy. Uses the inverse function theorem: if x = L^-1(y), then d(L^-1)/dy (y) = 1 / L'(x) evaluated with the EXACT Langevin derivative (not an approximant's derivative), at the highly accurate x produced by InverseLangevinAccurate. This is far more accurate than differentiating a closed-form approximation analytically (e.g. InverseLangevinDerivative, which inherits Cohen's ~5% approximation error) -- the error here is limited only by the Newton refinement in InverseLangevinAccurate, i.e. essentially full double precision away from y = +-1.

public static double InverseLangevinDerivative(
	double y,
	int newtonSteps = 3
)