Voxel position
Torch and numpy calculate voxel positions differently than assumed, such that frequency 0 is always contained: fftfreq(4) = [0.0, 0.25, -0.5, -0.25, 0.0] fftfreq(5) = [0.0, 0.2, 0.4, -0.4, -0.2]
Use fftshift(fftfreq) for voxelpositions in VoxelGridPhantom and reco_adjoint for maximum compatibility between adjoint and fft reco