Don't spin the executor if the sim is paused

[christophfroehlich]

After the refactoring done by ros-controls/ros2_control#1638, the switch_controller service has a working timeout for each controller. This time is hardcoded within the spawner.py to 5s.

If the simulation is started paused, like with

    gazebo = IncludeLaunchDescription(
                PythonLaunchDescriptionSource([os.path.join(
                    get_package_share_directory('gazebo_ros'), 'launch'), '/gazebo.launch.py']),
                launch_arguments={
                    'pause': 'true'}.items()
             )

then the CM services are started but the update method is not called yet. This leads to running into the timeout

[gzserver-5] [ERROR] [1727713930.188912404] [controller_manager]: Switch controller timed out after 5.000000 seconds!
[spawner-18] [ERROR] [1727713930.190697406] [spawner_joint_state_broadcaster]: Failed to activate controller

The same happens if a running simulation is paused and a service call to the CM is done.

As there is currently no possibility to pause the services in the CM, I see the possibility to just not spin the executor. Otherwise we have to change the API of the CM.

[christophfroehlich]

@mergify backport humble iron

[mergify]

backport humble iron

🟠 Waiting for conditions to match

• merged [📌 backport requirement]

[saikishor]

LGTM
Thank you for the fix!

[ahcorde]

Suggested change

	if (impl_->parent_model_->GetWorld()->IsPaused() == false) {
	if (!impl_->parent_model_->GetWorld()->IsPaused()) {

[christophfroehlich]

This approach does not work with the rolling version of the controller_manager, because it expects the URDF via topic. And one can't press the play button if the configure() method of the plugin is not finished.
I opened #380