L1Calo eFEX BDT-based tau algorithm integration
In additional to the existing tau algorithm, a BDT-based tau algorithm is added to the L1CaloFEXSim package. It simulates the algorithm implemented in https://gitlab.cern.ch/atlas-l1calo-efex/eFEXFirmware/-/merge_requests/298.
This will produce two additional eFexTauRoI_v1 EDMs in the output files (one for TOBx and another for xTOBs) containing the BDT algorithm's output.
The algorithm loads a json bdt configuration file located at data/bdt_config.json which contains all BDT weights and other relevant configuration.
The https://github.com/nlohmann/json library (MIT License, single file nlohmann/json.hpp in include dir) is used to read the json file. Due to how it works, the ATLAS class member naming conventions (starts with m_) cannot be applied there.
A unit test verifying that the BDT variables and scores are properly computed is also added.