Reduce memory peak
This update reduces the memory peak by: Nx * 2Ny * 2Nz * 2 * 8 bytes, e.g. 512MB (4383MB -> 3870MB) for (8196,32,32)
We need to be confident that this changes does not introduce errors, but it changes the order of the random numbers which makes the final boxes different. We therefore need some tests to check the spectra and statistics or a carefull review