Module materializer 

PhysicalPlanMaterializer: converts an arena PhysicalPlan into a StreamingExecutor tree.

This is the single instantiation path for all production queries:

Arc<PhysicalPlan> + QueryBindings
  -> validate
  -> allocate runtime + state arenas
  -> build operator tree per fragment
  -> return root StreamingExecutor

Structs

PhysicalPlanMaterializer

Converts an arena PhysicalPlan into a StreamingExecutor tree.