[yeseorizi]

Summary

Add the missing one-way Gazebo → ROS /clock bridge to the standalone REXROV and Slocum glider robot configurations.

On main (0d19c3f), Gazebo can be running while a ROS node with use_sim_time=true remains at time zero for these examples. Both configurations omit the clock mapping.

• Add /clock@rosgraph_msgs/msg/Clock[gz.msgs.Clock to each configuration.
• Add a regression test requiring exactly one one-way clock mapping and register it with ament/CTest, so normal package testing runs it.
• No simulator dynamics, controller, dependency or other robot configuration changes.

Reproduction and validation

• New configuration tests fail for both baseline configurations and pass with the mapping.
• Independently built this branch's robot-model package: 48 registered Python cases passed in 10 repeats (480 case executions).
• Independent runtime reruns received 20 increasing ROS clock samples and 10 odometry messages for each robot (REXROV clock: 0.127–0.146 s; Slocum: 3.290–3.309 s), with no residual simulator processes. The scene runs used a local diagnostic ros_gz_bridge shutdown overlay, which is not part of this PR.
• Changed-file pre-commit checks passed.

colcon build --packages-select posim_robot_models --cmake-args -DBUILD_TESTING=ON
ctest --test-dir build/posim_robot_models --output-on-failure \
  -R '^test_' --repeat until-fail:10

Scope / limitations

Tested in Ubuntu 26.04 ARM64 Docker on an Apple Silicon Mac, ROS 2 Lyrical / Gazebo Jetty 10.5.0. This covers the documented standalone launches, not a multi-world/multi-clock configuration or full-release validation.

The existing locally patched asv_wave_sim dependency also remained installed during scene checks. Neither that renderer teardown patch nor the bridge overlay is included in this PR; successful scene cleanup is not attributed to this change alone.

Checklist

• Forked the repository and kept the change focused.
• Added and registered regression tests; ran the package's Python tests and changed-file pre-commit.
• Signed commits with DCO and disclosed AI assistance.
• Whole repository colcon test / all platforms validated (outside this scoped fix).
• Remote formatting CI passed. Docker jobs are intentionally skipped for fork PRs; this is not a Docker build result. The website static-site check also passed; publishing was skipped.

Assisted-by: OpenAI Codex (implementation, tests and PR preparation).