Fix Rolling CI: migrate from ament_target_dependencies to target_link_libraries

[bburda]

Bug report

Rolling CI fails on build because ament_target_dependencies was removed from ament_cmake in Rolling.

Steps to reproduce

1. Push any commit to a branch with CI
2. Observe build-and-test (rolling, ubuntu:noble) job failure

Expected behavior

Rolling build succeeds (currently continue-on-error: true so it's non-blocking).

Actual behavior

CMake Error at CMakeLists.txt:59 (ament_target_dependencies):
  Unknown CMake command "ament_target_dependencies".

Fails in ros2_medkit_serialization (and would fail in all other packages too).

Environment

• ros2_medkit version: main (HEAD)
• ROS 2 distro: Rolling
• OS: Ubuntu Noble (24.04)

Additional information

28 occurrences across 7 CMakeLists.txt files need migration:

• ros2_medkit_gateway/CMakeLists.txt (5 occurrences)
• ros2_medkit_serialization/CMakeLists.txt (4 occurrences)
• ros2_medkit_fault_manager/CMakeLists.txt (5 occurrences)
• ros2_medkit_diagnostic_bridge/CMakeLists.txt (3 occurrences)
• ros2_medkit_fault_reporter/CMakeLists.txt (2 occurrences)
• ros2_medkit_integration_tests/CMakeLists.txt (9 occurrences)

The replacement is target_link_libraries with proper CMake targets. See ROS 2 Rolling ament_cmake docs.

Consider adding a compat shim in cmake/ROS2MedkitCompat.cmake that defines ament_target_dependencies as a wrapper around target_link_libraries on Rolling, to avoid touching every CMakeLists.txt.