compiler: Actually use ReportProcPlanner trait

CadrProcPlanner didn't actually extend ReportProcPlanner and due to code
drift their apply() signatures no longer matched. This is harmless now
but will become a problem once there are multiple report proc planners.

Bring them back in sync, make CadrProcPlanner extend ReportProcPlanner
and properly type the ReportProcPlanner list in PlanExpression.