Rails from Copper, and faster minecarts

Make the regular rails require 6 copper ingots instead of 6 iron. As well as make minecarts 2x faster

This simple change adresses 2 problems: Copper being "useless" and Minecarts being "useless"

If minecarts would be faster and rails would be crafted from copper, players will have a reason to back to the mines and search for copper, and because copper is the easiest by far ore to get, crafting rails would be worth it.

This additon would fit nicely in the Tinkering update that 1.21 is supposed to be