Mirror of microros_pub for the receive direction. Creates a node,
subscribes to /nuttx_sub with std_msgs/Int32, drives an rclc_executor
spin loop, and prints each received value. Exercises the new
rclc_executor + subscription callback path on top of the
microros_transport library shipped in apps/system/microros.
Validates the NuttX-native transport in the agent->client direction
end-to-end against a micro-ROS agent + ros2 topic pub on the host.
Signed-off-by: Arjav Patel <arjav1528@gmail.com>
