Improve List performance

class List is widely used across the project.

Basically it overperforms arrays in pushing speed.

However several improvements may still be made:

• Currently the node body stores a pointer, not the value itself. We can incapsulate the value without breaking the workflows (a double-pointer returned by ptr() is not actually needed anywhere)
• We can transform the structure to store the data in blocks linked in a list, instead of single nodes to reduce memory footprint. The blocks can be double-linked since the footprint will now become insignificant

Theer