Rolling back to a standard array for FA2 Barnes-Hut
There is currently no way to determine the maximum size of the array containing the Barnes-Hut tree. As such, if we keep a byte array to hold the tree and if we must therefore determine a fixed length for it at startup, we cannot avoid some edges cases to fail.

Since our tests proved that there were no significant performance change here between the use of standard arrays and byte arrays, we rolled back to the latter ones for safety.