implement INode for ROS2Node

[Deric-W]

Is your feature request related to a problem? Please describe. Writing nodes which are independent of Unity is problematic because the class Node used by ros2cs is not sharing any interfaces with the class ROS2Node used by this project, preventing nodes from accepting both.

Describe the solution you'd like ros2cs contains an interface called INode which represents a ROS2 Node which should include ROS2Node.

Describe alternatives you've considered

1. Writing Unity specific versions
   • code duplication
   • unnecessary work
2. Replacing ROS2Nodewith Node
   • might prevent nodes from being removed by the garbage collector
   • existing code would break
3. exposing the wrapped Node
   • would make usage a bit more cumbersome
   • would allow for using features not proxied by ROS2Node