Takes the 2 logarithm of a rank 0 STensor.
Given a real rank-0 STensor, returns its base-2 logarithm.
References syten::STensorImpl::STensor::autodiff_enabled(), syten::STensorImpl::STensor::get_and_renew_autodiff(), if_constexpr, imag(), std::log(), log2(), syten::STensorImpl::STensor::rank(), real(), syten::STensorImpl::STensor::set_autodiff_node(), SYTEN_ASSERT, SYTEN_TENSOR_RANK, and syten::STensorImpl::STensor::visit().
Referenced by syten::closest_power_two(), log2(), syten::Tensor< rank >::reduce(), and syten::von_neumann_entropy().