Fix FilePath service callbacks hanging in nvblox node

[shenfangqi123]

Summary

This PR fixes FilePath-based services in NvbloxNode hanging indefinitely when called from ROS 2.

In release-3.2, services such as save_map, save_rates, and save_ply can enter their callbacks, but the ROS 2 client may never receive a response. During debugging, it was observed that FilePath service requests could block while waiting for queued work to complete, causing the service call to hang indefinitely in a component container setup.

This change:

• Uses explicit 3-argument service callbacks for FilePath services.
• Executes FilePath save/load operations directly in the service callbacks.
• Avoids waiting on queued work from within the service callback.

Testing

Tested with Isaac ROS Nvblox release-3.2 using component_container_isolated.

Before this change:

• /nvblox_node/save_rates hangs indefinitely
• /nvblox_node/save_map hangs indefinitely
• /nvblox_node/save_ply hangs indefinitely

After this change:

• save_rates returns success=True
• save_map returns success=True and successfully writes a .nvblx file
• save_ply returns normally instead of hanging

Test Commands

ros2 service call /nvblox_node/save_rates \
nvblox_msgs/srv/FilePath \
"{file_path: '/tmp/rates.txt'}"

ros2 service call /nvblox_node/save_map \
nvblox_msgs/srv/FilePath \
"{file_path: '/workspace/.../test.nvblx'}"

ros2 service call /nvblox_node/save_ply \
nvblox_msgs/srv/FilePath \
"{file_path: '/workspace/.../test.ply'}"

Reproduction

The issue can be reproduced with:

ros2 service call /nvblox_node/save_rates \
nvblox_msgs/srv/FilePath \
"{file_path: '/tmp/rates.txt'}"

ros2 service call /nvblox_node/save_map \
nvblox_msgs/srv/FilePath \
"{file_path: '/tmp/test.nvblx'}"

ros2 service call /nvblox_node/save_ply \
nvblox_msgs/srv/FilePath \
"{file_path: '/tmp/test.ply'}"