TrigDecisionTool: remove DecisionObjectHandle classes
This is a more radical attempt at getting rid of the internal caching in the unpacker classes which was attempted in !49569 (merged) and had to be reverted due to performance issues in !49733 (merged). I think most of the code is historic and given we have universal support for ReadHandle in both the athena and the analysis release, there is probably no good reason to have a separate DecisionObjectHandle anymore.
So this MR removes the DecisionObjectHandle classes and instead uses a ReadHandle
directly in the unpacker classes. Also make the unpackers stateless and
move the logic if the decision (navigation) was already unpacked into CacheGlobalMemory.