### Description

expanding tasks in batches to allow mapped tasks spawn more than 1024 processes.

### Use case/motivation

Maximum length of a list is limited to 1024 by `max_map_length (AIRFLOW__CORE__MAX_MAP_LENGTH)`.
during scheduling of the new tasks, an UPDATE query is ran that tries to set all the new tasks at once.  Increasing `max_map_length` more than 4K makes airflow scheduler completely unresponsive.

Also, Postgres throws `stack depth limit exceeded` error which can be fixed by updating to a newer version and setting `max_stack_depth` higher. But it doesn't really matter because airflow scheduler freezes up.
 
As a workaround, I split the dag runs into subdag runs which works but it would be much nicer if we didn't have to worry about exceeding  `max_map_length`. 

### Related issues

It was discussed here:
[Increasing 'max_map_length' leads to SQL 'max_stack_depth' error with 5000 dags to be spawned #28478](https://github.com/apache/airflow/discussions/28478)

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

"""
        The mini-scheduler for scheduling downstream tasks of this task instance
        :meta: private
        """
        from sqlalchemy.exc import OperationalError
        from airflow.models import DagRun
        try:
            
            dag_run = with_row_locks(
                session.query(DagRun).filter_by(
                    dag_id=self.dag_id,
                    run_id=self.run_id,
                ),
                session=session,
            ).one()
            task = self.task
            if TYPE_CHECKING:
                assert task.dag
            
            
            
            partial_dag = task.dag.partial_subset(
                task.downstream_task_ids,
                include_downstream=True,
                include_upstream=False,
                include_direct_upstream=True,
            )
            dag_run.dag = partial_dag