New functors to place objects in a vector and to concatenate two vectors

This MR defines two new functors:

• SINGLE : takes an object of type T and return a std::vector<T> containing such object
• CONCATENATE : takes two vectors v1,v2of the same type std:vector<T> and return a single std:vector<T> with { v1_elements, v2_elements }

This will help to distinguish two particles with same ID and Charge when using ThorParticleSelection , for example to compute ConeIsolation variables around each final state track

fields = {
        "Tau"   :   "[tau+ -> mu+ mu+ mu-]CC",
        "L1"  :     "[tau+ -> ^mu+ mu+ mu-]CC",
        "L2"  :     "[tau+ -> mu+ ^mu+ mu-]CC",
        "L3"  :     "[tau+ -> mu+ mu+ ^mu-]CC",
}

data = get_particles(f"/Event/HLT2/Hlt2RD_TauToMuMuMu/Particles")
L1_data = ThOrParticleSelection(
        InputParticles=data, Functor=F.SINGLE @ F.VALUE @ F.FIND_DECAY(fields["L1"])
    ).OutputSelection