fix: type stability of vt_stability VTStabilityResult #65
Description
@code_warntype vt_stability(mixture, nmol, volume, CubicEoS.GAS_CONSTANT_SI * t, stabopts.variables; maxiter=stabopts.maxiter, tol=1e-6)
Body::Tuple{Bool, Bool, NTuple{4, CubicEoS.VTStabilityResult}} # in red!