Addition of two one-site operators acting on the same site.
References syten::IPEPSv2::AOneOp::aux, syten::STensorImpl::expand(), syten::STensorImpl::gen_combinator(), syten::IPEPSv2::AOneOp::loc, syten::IPEPSv2::AOneOp::op, syten::IPEPSv2::AOneOp::phys_inp, syten::IPEPSv2::AOneOp::phys_out, and SYTEN_ASSERT.
Referenced by syten::T3N::State::add(), syten::Tensor< rank >::add(), syten::T3N::apply_operator_itrunc(), syten::cacheFilename(), syten::Pyten::init_ipeps_lattice(), operator+(), operator+=(), operator-(), and operator-=().