Ctor initialising an empty tensor of the same rank as bases
has entries and, if specified, the given fermionic order (ascending otherwise).
References bases, std::vector< T >::begin(), std::vector< T >::end(), fermionic_order, std::iota(), rank(), syten::STensorImpl::registry_enter_stensor(), std::vector< T >::resize(), sanity_check_bases(), and std::vector< T >::size().