Method on_comp_node_finalize

imperative/src/impl/physical_tensor.cpp:458–462

    struct Guard final : CompNodeDepedentObject {
        std::shared_ptr<void> on_comp_node_finalize() override {
            MGB_LOCK_GUARD(mtx);
            inst.reset();
            return {};
        }
    };

    static std::optional<Guard> guard;