Callback fired synchronously or asynchronously after a transformation successfully completes.
Extends TransformationHookContext with three additional fields:
inputCount— rule count entering the transformationoutputCount— rule count exiting the transformationdurationMs— wall-clock execution time
Useful for: timing metrics, rule-count diff reporting, telemetry.
(context: TransformationHookContext & { inputCount: number; outputCount: number; durationMs: number; }) => void | Promise<void>