Unify key4hep

[farakiko]

Addressing issue #333
(Also fixes minor bug regarding the tfds dataset splitting for pipelines where ntrain/nvalid are given.)

Changes

• Wrote a new postprocessing.py script to unify the postprocessing of events generated with key4hep under the EDM4HEP format
• The new script can be run with the following choices for --dataset [clic, fcc]

The following commands were tested:

For FCCee dataset postprocessing
python mlpf/data/key4hep/postprocessing.py --input /pfvolcentral/data/cld_key4hep/2024_05_full/p8_ee_tt_ecm365/root/reco_p8_ee_tt_ecm365_100038.root --outpath /pfvolcentral/data/cld_key4hep/2024_05_full/p8_ee_tt_ecm365/raw/p8_ee_tt_ecm365/ --dataset fcc

tfds build mlpf/heptfds/cld_pf_edm4hep/ttbar --manual_dir /pfvolcentral/data/cld_key4hep/2024_05_full/p8_ee_tt_ecm365/raw/

For CLIC dataset postprocessing
python mlpf/data/key4hep/postprocessing.py --input /pfvolcentral/data/clic_key4hep/2024_07/gamma/root/ --outpath /pfvolcentral/data/clic_key4hep/2024_07/gamma/raw/gamma/ --dataset clic

References:
Breaking changes that have been introduced in EDM4hep v1.0

• key4hep/EDM4hep#326: the variable radiusOfInnermostHit was removed (the current PR creates the variable manually and was validated using the old files that had this branch present.)
• key4hep/EDM4hep#341: the associations to links were renamed. CaloHitLinks have been renamed as follows reco->from and sim->to
• key4hep/EDM4hep#311: the dEdx variable has been renamed to dQ/dx and moved under different collection (from SiTracks_Refitted to SiTracks_Refitted_dQdx)

The full list of all breaking changes is listed here: key4hep/EDM4hep#261