ns-export gaussiansplatting ply property ordering

[mathijshenquet]

Is your feature request related to a problem? Please describe.
The order of the properties in a ply file should not matter, but some tools like aras-p/UnityGaussianSplatting do require a predetermined property order. See here.
The ordering of the ply file produced by ns-export appears to be random and is thus incompatible with aras-p's project.

Describe the solution you'd like
Make the order of the exported ply conform to the one from original inri implementation for general backward compatibility.

Describe alternatives you've considered
Ideally the parsing code in UnityGaussianSplatting should be fixed