cpp/numeric/special functions/sph neumann

@1-3@ Computes the, also known as the spherical Neumann function, of and. @A@ Additional overloads are provided for all integer types, which are treated as.

Return value
If no errors occur, returns the value of the spherical Bessel function of the second kind (spherical Neumann function) of and, that is $n n(x) = (π/2x)1/2 N n+1/2(x)$ where $N n(x)$ is  and $x≥0$.

Error handling
Errors may be reported as specified in math_errhandling
 * If the argument is NaN, NaN is returned and domain error is not reported
 * If $n≥128$, the behavior is implementation-defined