investigate performance of createTreeFromElements in SszCollectionSchema

[rolfyone]

There was a todo regarding performance in the code, this is going to be the more permanent to suggest that the code could likely be more efficient.

Code is commented as

    // This is a generic implementation which works for both Vector and List but it potentially
    // could do better if construct the tree directly in List/Vector subclasses

and i'll add this ticket as a reference to the code block