### 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/operator/BatchEncoder.java
@Override
        public void decode(Block.Builder builder, IsNull isNull, BytesRef[] encoded, int count) {
            IntBlock.Builder b = (IntBlock.Builder) builder;
            for (int i = 0; i < count; i++) {
                if (isNull.isNull(i)) {
                    b.appendNull();
                } else {
                    BytesRef e = encoded[i];
                    b.appendInt((int) intHandle.get(e.bytes, e.offset));
                    e.offset += Integer.BYTES;
                    e.length -= Integer.BYTES;
                }
            }
        }
    }
    private static final VarHandle longHandle = MethodHandles.byteArrayViewVarHandle(long[].class, ByteOrder.nativeOrder());
    protected abstract static class Longs extends BatchEncoder {