API of RealtimeBox is broken

[christophfroehlich]

• ur_controller: https://github.com/UniversalRobots/Universal_Robots_ROS2_Driver/pull/1189
• ros2_controllers: https://github.com/ros-controls/ros2_controllers/actions/runs/11988629468/job/33424120547 fixed with https://github.com/ros-controls/ros2_controllers/pull/1385

the deprecation failed, things to fix

• [x] The set/get method is not compatible any more, @saikishor has an idea
• [x] received_velocity_msg_ptr_.set(nullptr); like we used in diff_drive_controller now builds but throws C++ exception with description "bad_function_call" thrown in the test body. at runtime
• [x] the realtime_box_best_effort.h is not available any more -> add it again pointing to the new one with a deprecation warning
• [x] add downstream builds to a CI job to be more aware of API breaking changes https://github.com/ros-controls/realtime_tools/pull/201

Not sure if we can fix that for the humble releases, or we have to revert that and branch for rolling.