Hello,

I want to add some custom data into tensor,

And I will use this in some function I write,

For now, I want it keep unchanged when I copy a tensor, what should I do?

currently, I add `Eigen::array<Leg, DerivedTraits::NumDimensions> leg_info;` in `class TensorBase`,

add many `this->leg_info = other.leg_info` in different places, It seems it is not a good way,

so, what is the proper way to achieve this goal?

the detail is in https://paste.ubuntu.com/p/zKZX9Bxn6d/