make const in ElectronPhotonFourMomentumCorrection and interface (part 3 of ticket ATLASG-2729)
requested to merge turra/athena:ATLASG-2729-ElectronPhotonFourMomentumCorrection-simplify-random-smearing-tris into main
This is the last part of the changes in ElectronPhotonFourMomentumCorrection to have the main functions const. No output changed, as seen from the tests introduced in !72295 (merged).
This closes ATLASG-2729.