### 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
"""Heartbeat sent to trigger new jobs."""
        if not self.parallelism:
            open_slots = len(self.queued_tasks)
        else:
            open_slots = self.parallelism - len(self.running)
        num_running_tasks = len(self.running)
        num_queued_tasks = len(self.queued_tasks)
        self.log.debug("%s running task instances", num_running_tasks)
        self.log.debug("%s in queue", num_queued_tasks)
        self.log.debug("%s open slots", open_slots)
        Stats.gauge("executor.open_slots", open_slots)
        Stats.gauge("executor.queued_tasks", num_queued_tasks)
        Stats.gauge("executor.running_tasks", num_running_tasks)
        self.trigger_tasks(open_slots)
        
        self.log.debug("Calling the %s sync method", self.__class__)
        self.sync()
    def order_queued_tasks_by_priority(self) -> list[tuple[TaskInstanceKey, QueuedTaskInstanceType]]:
        """
        Orders the queued tasks by priority.
        :return: List of tuples from the queued_tasks according to the priority.
        """
        return sorted(
            self.queued_tasks.items(),
            key=lambda x: x[1][1],
            reverse=True,
        )
    def trigger_tasks(self, open_slots: int) -> None: