Lists and tuples' ambiguous behavior when used recursively

In sdk/variable.go of the sdk repository, the List[T CircuitVariable] type itself implements CircuitVariable. However, should lists be nested, in the following implementation of FromValues, the loop will never terminate, as fresh lists are empty — so nv will be zero.

func (l List[T]) FromValues(vs ...frontend.Variable) CircuitVariable {
	typ := *new(T)
	nv := int(typ.NumVars())
	for i := 0; i < len(vs); i += nv {
		values := vs[i : i+nv]
		l[i] = l[i].FromValues(values...).(T)
	}
	return l
}

Additionally, the above implementation of FromValues will also fail for any other types implementing CircuitVariable, unless all the components of the list have the same positive number of field elements and this size is also the same as the size of the default of type T.

Similarly, tuples can also not have components that are lists, for the same reason.

We recommend to clearly document these limitations.