Access to tree.Jet in src/definitions.py: possible source of errors

[fiemmi]

Calling tree.Jet in src/definitions.py (this line) will access different jet collections depending on the input sample. The Jet collection is CHS in Run2 samples and PUPPI in Run3 samples. This may cause users to retrieve jet collections inconsistently.

Things can get more complicated when accessing non-standard flavors of NanoAOD, e.g. JMENano where both PUPPI and CHS are available, or custom JMENano with additional ABC collections. A way to deal with this (more elegant than hard-coding the collections to be retrieved) may be needed.