### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

all

### Problem Description

Do this

### Steps to Reproduce

```
rm /tmp/evil
for a in {0..9}; do
   for b in {0..9}; do
      echo '{"index": {}}' >> /tmp/evil
      echo '{"a": '$a', "b": '$b'}' >> /tmp/evil
   done
done
echo >> /tmp/evil

curl -uelastic:password -XDELETE localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPUT localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_bulk --data-binary @/tmp/evil
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_forcemerge?max_num_segments=1
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_refresh

curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/_esql?pretty -d'{
   "query": "FROM test | STATS MAX(a) BY a, b | KEEP a"
}'
```

### Logs (if relevant)

_No response_
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/planner/LocalExecutionPlanner.java
* The count and type of driver parallelism.
     */
    record DriverParallelism(Type type, int instanceCount) {
        DriverParallelism {
            if (instanceCount <= 0) {
                throw new IllegalArgumentException("instance count must be greater than zero; got: " + instanceCount);
            }
        }
        static final DriverParallelism SINGLE = new DriverParallelism(Type.SINGLETON, 1);
        enum Type {
            SINGLETON,
            DATA_PARALLELISM,
            TASK_LEVEL_PARALLELISM
        }
    }
    /**
     * Context object used while generating a local plan. Currently only collects the driver factories as well as
     * maintains information how many driver instances should be created for a given driver.
     */
    public record LocalExecutionPlannerContext(
        List<DriverFactory> driverFactories,
        Holder<DriverParallelism> driverParallelism,
        int taskConcurrency,
        DataPartitioning dataPartitioning,
        int configuredPageSize,
        BigArrays bigArrays,
        BlockFactory blockFactory
    ) {
        void addDriverFactory(DriverFactory driverFactory) {
            driverFactories.add(driverFactory);