ElectronPhotonSelectorTools: replace snprintf with std::format

Frank Winklmeierrequested to merge
fwinkl/athena:eleselector into main

Use std::format for string formatting and remove unnecessary array initialization loop (it is default initialized). In addition, fix unnoticed bug in the forward LH introduced in !76307 (merged).

Also fixes cppcheck false positive in ARM build.

Edited by Frank Winklmeier

Merge request reports