feat: add synthetic slam odometry publisher

[lblommesteyn]

Problem
The mapping pipeline can bridge /slam_odom into AP1 localization and odometer topics, but smoke tests currently need a real SLAM odometry source before downstream planning can receive odometer data.

For RealSense bag bringup and integration testing, it is useful to exercise the mapping -> planning data path before Kitware SLAM/localization is fully configured.

Changes

• Add synthetic_slam_odom_publisher_node, which publishes deterministic nav_msgs/Odometry on /slam_odom.
• Add a use_synthetic_odometry launch flag to mapping_pipeline.launch.py.
• Add launch parameters for synthetic odometry publish rate and forward speed.
• Document the smoke-test launch mode.

Notes
This is explicitly for smoke tests and does not replace real localization. Together with mapping-and-localization#10, this can provide planner's odometer input during bag/integration tests when no live SLAM source is available.

Test plan

• python3 -m py_compile mapping_localization_python/mapping_localization_python/synthetic_slam_odom_publisher_node.py mapping_localization_python/launch/mapping_pipeline.launch.py mapping_localization_python/setup.py
• git diff --check