Draft: Prevent CP algorithms from copying the EventInfo collection
In general we only want to have 1 EventInfo container. Right now there are a few algorithms apply weight decorations to the EventInfo which depend on systematics. This MR switches those to use SysDecorationHandles. The most involved one of these is the pileup reweighting alg. This required me to make a small (backwards compatible) change in the tool's interface so that the methods used in apply could be extracted into the algorithm's body.
This also adds a new ctest to run the pileup reweighting. I've checked that all the existing ctests run correctly.
This includes a change to the SysDecorationHandle to make it possible to decorate const containers. Apparently a sweep from release 22 is due that will also do this, so when that is in I'll resolve that conflict and remove the Draft.