On each batch we load through DocumentSourceCursor, we will accidentally bump the keysExamined and docsExamined instead of resetting them to zero and then re-computing them.

More specifically, Explain::getSummaryStats() is called (indirectly) during DocumentSourceCursor::loadBatch(). That will increment the totalKeysExamined and totalDocsExamined for each stage, but these were never reset to 0, so it will double count the first batch.