### Description

![image](https://github.com/elastic/elasticsearch/assets/76245/d0443170-0419-4759-b505-7620ff3d6594)

The execution time of grouping stats by multiple keywords has increased: 1.2 to 1.6 seconds (with doc_partitioning), 4.3 to 6.7 seconds (with shard_partitioning). The equivalent query with the _search API takes 1.8 seconds.

`from nyc_taxis | ... | stats c = count(dropoff_datetime) by trip_type, payment_type, vendor_id`

This regression occurred since July 2, 2023, and I suspect it may be due to the PR: [Support multivalued fields on arbitrary grouping](https://github.com/elastic/elasticsearch-internal/pull/1340).

/cc @nik9000
x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/aggregation/blockhash/PackedValuesBlockHash.java
final HashAggregationOperator.GroupSpec spec;
        BatchEncoder encoder;
        int positionOffset;
        int valueOffset;
        int loopedIndex;
        int valueCount;
        int bytesStart;
        Group(HashAggregationOperator.GroupSpec spec) {
            this.spec = spec;
        }
    }
    class AddWork extends LongLongBlockHash.AbstractAddBlock {