Selection framework improvements

• Introduce new "combination of particle" types Sel::ParticleCombination (something like std::tuple<Ts...>) and Sel::ParticleCombinationSpan (something like LHCb::span<std::variant<Ts...>>
• Retire older, less flexible Phys/SelKernel/SelKernel/TrackCombination.h in favour of Sel::ParticleCombination
• Simplify functor adapters like SUM, MAX, ... using new Sel::ParticleCombination utilities
• Fix trivial bug in DistanceOfClosestApproachChi2Cut
• Reorganise some type_trait helpers
• Add feature to the ThOr functor interface to allow the compilation (JIT/cache/both) behaviour to be tweaked per-functor
• Allow the two state-like arguments to LHCb::TrackVertexUtils::vertexChi2() to have different types, and make the function body slightly more generic.
• Add an extra check to Tr/TrackUtils/tests/src/TestZipInfrastructure.cpp

Should be applied with Phys!734 (merged)

cc: @nnolte