OuNion OrdVectoru merge inplace

[kilohsakul]

Hm, doing this with the two input vectors only does not seem so easy.

Instead, this is maybe a place where a static reusable data structure would makse sense.
Merge the two into a static third vector, and then coppy the third vector to, say, lhs vector.
This only requires to sometimes resize the lhs.

Btw, if the underlying data struct was a dequeue, then one could just concatenate the lhs and rhs and coppy the merged data there, no allocation would be needed.
Maybe we could try sometime what this does.