Unify key4hep (#374)

* up first version of unified postprocessing

* must remove ECALother from fcc

* include MCParticles.PDG for fcc

* remove MCParticles#1.index from fcc

* remove "index": prop_data["MCParticles#1.index"][iev]

* fix daus index

* rename dir to key4hep

* add option to postprocess a directory at once

* up tfds script for fcc

* copy utils script

* add BUILDER_CONFIGS

* add NUM_SPLITS

* add gamma to heptfds

* must fix the track state

* up radiusOfInnermostHit

* add proper event splitting for ntrain and nvalid

* linting