Unnecessary use of SkipListAccessor in TPRequestHandler::periodic_data_transmission() ?

https://github.com/DUNE-DAQ/trigger/blob/6b62c0c62670ba00016e7ce5163e0c8cefe96f66/src/TPRequestHandler.cpp#L65

My understanding of SkipList node removal is that it is done lazily, removing nodes that have been marked for removal only after all SkipListAccessors, so creating accessors more than needed induces some overhead and may reduce some ability to get cleanup done.

I don't know if removing this will help much with the performance issue noted here https://github.com/DUNE-DAQ/datahandlinglibs/issues/62, but I don't think the accessor created here is really necessary: get_fragment_pieces() will create an accessor when it gets its lower_bound iterator, and so if we only need to get the best understanding of the timestamps, then we should be able to call front() and back() here (as is done in other datahandling places).

If others agree, we might try to remove this here, and then see if that helps (or at least doesn't hurt) the cleanup situation.

Start in src/TPRequestHandler.cpp at periodic_data_transmission() and inspect how get_fragment_pieces() creates its SkipListAccessor through lower_bound. Compare that with the existing front() and back() usage in other datahandling locations. Done means determining whether the extra accessor can be removed without changing timestamp handling, then checking the datahandlinglibs issue for relevant performance effects.