### 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
"""Number of new tasks this executor instance can accept."""
        if self.parallelism:
            return self.parallelism - len(self.running) - len(self.queued_tasks)
        else:
            return sys.maxsize
    @staticmethod
    def validate_command(command: list[str]) -> None:
        """
        Back-compat method to Check if the command to execute is airflow command.
        :param command: command to check
        """
        warnings.warn(
            """
            The `validate_command` method is deprecated. Please use ``validate_airflow_tasks_run_command``
            """,
            RemovedInAirflow3Warning,
            stacklevel=2,
        )
        BaseExecutor.validate_airflow_tasks_run_command(command)
    @staticmethod
    def validate_airflow_tasks_run_command(command: list[str]) -> tuple[str | None, str | None]: