Write a Python launch file for ROS 2 (Lyrical Luth) that starts multiple nodes with namespaces, arguments and topic remappings

Documented steps

1. Source ROS 2 in every new terminal (`source /opt/ros/lyrical/setup.bash`), then `mkdir launch`.
2. Create launch/turtlesim_mimic_launch.py starting with `from launch import LaunchDescription` and `from launch_ros.actions import Node`, then `def generate_launch_description(): return LaunchDescription([ ... ])`.
3. First Node action: Node(package='turtlesim', namespace='turtlesim1', executable='turtlesim_node', name='sim', arguments=['--ros-args', '--log-level', 'info']). `arguments` goes straight to the executable, so ROS-specific args need the explicit --ros-args flag.
4. Second Node action: Node(package='turtlesim', namespace='turtlesim2', executable='turtlesim_node', name='sim', ros_arguments=['--log-level', 'warn']). `ros_arguments` is for ROS-only args and needs no --ros-args flag.
5. Third Node action launches the turtlesim `mimic` executable with remappings=[('/input/pose', '/turtlesim1/turtle1/pose'), ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel')] so turtlesim2 mimics turtlesim1.
6. Give the two turtlesim_node instances distinct namespace= values to avoid node-name and topic-name conflicts.
7. Run it: `cd launch && ros2 launch turtlesim_mimic_launch.py`. Two turtlesim windows open and the terminal logs 'process started with pid [...]' for each of the three nodes.
8. Drive turtle1 to see the mimic effect: `ros2 topic pub -r 1 /turtlesim1/turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: -1.8}}"`.
9. Inspect the graph in a new terminal: `ros2 run rqt_graph rqt_graph`.
10. When the launch file lives inside a package, run it as `ros2 launch <package_name> <launch_file_name>` and add <exec_depend>ros2launch</exec_depend> to that package's package.xml.
11. Official doc: https://docs.ros.org/en/lyrical/Tutorials/Intermediate/Launch/Creating-Launch-Files.html