Add a StereoDispCombiner implementing DISP-based stereo direction reconstruction.
Adapted from the implementation in magic-cta-pipe and EventDisplay, it combines mono DISP reconstruction by: - get combinations of 2 telescope for every array event - calculating the minimum distance for the 4 possible SIGN pairs for each combination - DISP sign score can be optionally used to weight the distances - calculating the weighted average for the minimum distance SIGN pair (fov lon/lat) per combination - calculating the weighted average of all combinations for an array event with the summed weights