Add URDF model with RViz visualization and namespaced publisher launch files

[adityakamath]

Summary

• Adds a URDF/xacro model (urdf/rplidar.urdf.xacro) with mesh files for RPLIDAR A1/A2, and updates rviz/rplidar.rviz to display the robot model
• Adds new namespaced launch files for running the lidar alongside robot_state_publisher:
  • launch/rplidar_publisher.launch (publishes the lidar node under an ns namespace, replaces rplidar.launch)
  • launch/rplidar_publisher_desc.launch (publishes robot_description and TF for the lidar URDF)
  • launch/rplidar_publisher_viz.launch (RViz visualization including the robot model, replaces view_rplidar.launch)
• Updates CMakeLists.txt to install the new urdf directory
• Updates README.md to reference the new launch file names
• Removes accidentally committed .ipynb_checkpoints/ directories and adds a .gitignore to prevent recurrence

Notes

• rplidar.launch and view_rplidar.launch were renamed to rplidar_publisher.launch and rplidar_publisher_viz.launch respectively as part of this change; README references were updated accordingly
• The new rplidar_publisher.launch wraps the node in a <group ns="$(arg ns)">, so rosrun rplidar_ros rplidarNodeClient (which subscribes to the global /scan topic) will not receive messages unless remapped or run without the namespace — flagging this as a known caveat for reviewers

Test plan

• Build the package and run roslaunch rplidar_ros rplidar_publisher_viz.launch on an A1/A2, confirm RViz shows both the laser scan and the lidar model
• Run roslaunch rplidar_ros rplidar_publisher.launch and confirm the node starts and publishes scans under the rplidar namespace

Note: This PR description was generated with Claude Code assistance.