test_nodes: catch keyboard interrupt and add simple launch tests (backport #1369)

[mergify]

When the test nodes are shut down by ctrl-c keyboard interrupt we see this verbose console output

    [publisher_forward_position_controller-15] Traceback (most recent call last):
    [publisher_forward_position_controller-15]   File "/home/runner/work/ros2_control_demos/ros2_control_demos/.work/upstream_ws/install/ros2_controllers_test_nodes/lib/ros2_controllers_test_nodes/publisher_forward_position_controller", line 33, in <module>
    [publisher_forward_position_controller-15]     sys.exit(load_entry_point('ros2-controllers-test-nodes==3.28.0', 'console_scripts', 'publisher_forward_position_controller')())
    [publisher_forward_position_controller-15]   File "/home/runner/work/ros2_control_demos/ros2_control_demos/.work/upstream_ws/install/ros2_controllers_test_nodes/lib/python3.10/site-packages/ros2_controllers_test_nodes/publisher_forward_position_controller.py", line 71, in main
    [publisher_forward_position_controller-15]     rclpy.spin(publisher_forward_position)
    [publisher_forward_position_controller-15]   File "/opt/ros/iron/lib/python3.10/site-packages/rclpy/__init__.py", line 228, in spin
    [publisher_forward_position_controller-15]     executor.spin_once()
    [publisher_forward_position_controller-15]   File "/opt/ros/iron/lib/python3.10/site-packages/rclpy/executors.py", line 787, in spin_once
    [publisher_forward_position_controller-15]     self._spin_once_impl(timeout_sec)
    [publisher_forward_position_controller-15]   File "/opt/ros/iron/lib/python3.10/site-packages/rclpy/executors.py", line 776, in _spin_once_impl
    [publisher_forward_position_controller-15]     handler, entity, node = self.wait_for_ready_callbacks(timeout_sec=timeout_sec)
    [publisher_forward_position_controller-15]   File "/opt/ros/iron/lib/python3.10/site-packages/rclpy/executors.py", line 762, in wait_for_ready_callbacks
    [publisher_forward_position_controller-15]     return next(self._cb_iter)
    [publisher_forward_position_controller-15]   File "/opt/ros/iron/lib/python3.10/site-packages/rclpy/executors.py", line 666, in _wait_for_ready_callbacks
    [publisher_forward_position_controller-15]     wait_set.wait(timeout_nsec)
    [publisher_forward_position_controller-15] KeyboardInterrupt

With the proposed changes, we get a nice

 $ ros2 run ros2_controllers_test_nodes publisher_forward_position_controller --ros-args --params-file src/ros2_control_demos/example_1/bringup/config/rrbot_forward_position_publisher.yaml 
[INFO] [1731859611.015984561] [publisher_forward_position_controller]: Publishing 4 goals on topic '/forward_position_controller/commands' every 5 s'
[INFO] [1731859616.018749700] [publisher_forward_position_controller]: Publishing: "array('d', [0.785, 0.785])"
^CKeyboard interrupt received. Shutting down node.
```<hr>This is an automatic backport of pull request #1369 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

Attention: Patch coverage is 90.56604% with 10 lines in your changes missing coverage. Please review.

Project coverage is 66.27%. Comparing base (5fcc9fd) to head (e723cdd).
Report is 1 commits behind head on humble.

Files with missing lines	Patch %	Lines
...est_nodes/publisher_forward_position_controller.py	44.44%	4 Missing and 1 partial ⚠️
...est_nodes/publisher_joint_trajectory_controller.py	44.44%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #1371      +/-   ##
==========================================
+ Coverage   65.27%   66.27%   +1.00%     
==========================================
  Files         108      110       +2     
  Lines       12562    12662     +100     
  Branches     7805     7815      +10     
==========================================
+ Hits         8200     8392     +192     
+ Misses       1522     1415     -107     
- Partials     2840     2855      +15     

Flag	Coverage Δ
unittests	66.27% <90.56%> (+1.00%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ros2_controllers_test_nodes/setup.py	0.00% <ø> (ø)
...st_publisher_forward_position_controller_launch.py	100.00% <100.00%> (ø)
...st_publisher_joint_trajectory_controller_launch.py	100.00% <100.00%> (ø)
...est_nodes/publisher_forward_position_controller.py	80.43% <44.44%> (+80.43%)	⬆️
...est_nodes/publisher_joint_trajectory_controller.py	54.03% <44.44%> (+54.03%)	⬆️