Fix 1D and 2D domain scaling in the distributed benchmark

Created by: aprokop

Currently, the domains are constructed as [-a,a]^d, where d is the partition dimension, and a = std::cbrt(n_values). This way, the density of points stays constant in 3D. However, for 1D and 2D the density varies, and the same radius would produce different average results. The value of a should be set to n_values in 1D, and std::sqrt(n_values) in 2D.