HashAggregationOperator misreports memory usage after spilling

[findepi]

In some situations, when spilling occurs, HashAggregationOperator doesn't reset memory usage to 0 upon finishing.

Can be reproduced with io.trino.operator.TestHashAggregationOperator#testHashAggregationMemoryReservation

after adding assertions:

// this passes
assertEquals(getOnlyElement(operator.getOperatorContext().getNestedOperatorStats()).getRevocableMemoryReservation().toBytes(), 0);
// this fails in some cases:
assertEquals(getOnlyElement(operator.getOperatorContext().getNestedOperatorStats()).getSystemMemoryReservation().toBytes(), 0);

right after

assertEquals(getOnlyElement(operator.getOperatorContext().getNestedOperatorStats()).getUserMemoryReservation().toBytes(), 0);

cc @sopel39

[sopel39]

It will zero memory on close, bu I agree it should release on finished