### Overview
Some Executors, currently a subset of the local Executors, run in a single threaded fashion and have certain limitations and requirements, many of which are hardcoded. To add a new single threaded Executor would require changes to core Airflow code.
Note: This coupling often shows up with SQLite compatibility checks since it does not support multiple connections.
### Examples
- **2a**) SQLite check done in configuration.py: https://github.com/apache/airflow/blob/26f94c5370587f73ebd935cecf208c6a36bdf9b6/airflow/configuration.py#L412-L419
- **2b**) When running in standalone mode SQLite compatibility is checked: https://github.com/apache/airflow/blob/26f94c5370587f73ebd935cecf208c6a36bdf9b6/airflow/cli/commands/standalone_command.py#L160-L165
- **2c**) Sensors in `poke` mode can block execution of DAGs when running with single process Executors, currently hardcoded to DebugExecutor (although should also include SequentialExecutor): https://github.com/apache/airflow/blob/27e2101f6ee5567b2843cbccf1dca0b0e7c96186/airflow/sensors/base.py#L243
### Proposal
A static method or attribute on the Executor class which can be checked by core code.

There is a precedent already set with the `supports_ad_hoc_ti_run` attribute, see:
https://github.com/apache/airflow/blob/fb741fd87254e235f99d7d67e558dafad601f253/airflow/executors/kubernetes_executor.py#L435 https://github.com/apache/airflow/blob/26f94c5370587f73ebd935cecf208c6a36bdf9b6/airflow/www/views.py#L1735-L1737
"""End celery and kubernetes executor."""
        self.celery_executor.end()
        self.kubernetes_executor.end()
    def terminate(self) -> None:
        """Terminate celery and kubernetes executor."""
        self.celery_executor.terminate()
        self.kubernetes_executor.terminate()
    def _router(self, simple_task_instance: SimpleTaskInstance) -> CeleryExecutor | KubernetesExecutor:
        """
        Return either celery_executor or kubernetes_executor.
        :param simple_task_instance: SimpleTaskInstance
        :return: celery_executor or kubernetes_executor
        """
        if simple_task_instance.queue == self.KUBERNETES_QUEUE:
            return self.kubernetes_executor
        return self.celery_executor
    def debug_dump(self) -> None:
        """Called in response to SIGUSR2 by the scheduler."""
        self.log.info("Dumping CeleryExecutor state")
        self.celery_executor.debug_dump()
        self.log.info("Dumping KubernetesExecutor state")
        self.kubernetes_executor.debug_dump()
    def send_callback(self, request: CallbackRequest) -> None:
        """Sends callback for execution.
        :param request: Callback request to be executed.
        """
        if not self.callback_sink:
            raise ValueError("Callback sink is not ready.")
        self.callback_sink.send(request)