Make sure Functors::Optional is returned from functors, and not std::optional

There is a report that MUONCATBOOST causes:

ERROR Value type returned by functor not supported. Problematic ThOr functor : ::Functors::PID::MuonCatBoost{} with field name: L1_MUONCATBOOST

which implies that the return type of MuonCatBoost is not registered with FunTuple. Looking at the code, it looks like MuonCatBoost return std::optional instead of Functors::Optional -- this MR re-organizes a few things such that MUONCATBOOST (and a few other functors) return Functors::Optional instead.