DensifyStage already has a tracker. We will construct it via createChunkedSimpleMemoryUsageTracker, so it is chained to OperationMemoryUsageTracker, and thread it to the partition expression's evaluate method. The flags gFeatureFlagExpressionMemoryTracking and gFeatureFlagMemoryTracking must be checked before passing the tracker.

A MemoryUsage token will be created and updated for each generated document and the memory will be reduced when the document is returned since the stage is streaming and does not hold the document anymore.

As part of the expression memory tracking work, DensifyStage will serialise the tracker into the executionStats explain output.