Avoid using `rclcpp::detail::*` from agnocastlib (non-public / unstable API)

[sykwer]

rclcpp::detail::* is an internal (non-public) API in rclcpp and may change without notice across ROS 2 releases and even patch versions. We should avoid depending on it from agnocastlib.

See README at https://github.com/ros2/rclcpp/tree/rolling/rclcpp/include/rclcpp/detail.

Motivation / Problem

• Anything under rclcpp::detail is not part of the stable public API surface.
• Depending on it increases the risk of:
  • sudden build breaks when upgrading ROS 2 (e.g., Humble → Jazzy),
  • subtle runtime/ABI issues if internal behavior changes,
  • ongoing maintenance burden (tracking upstream refactors).