Add loaned message pub-sub test to test_tracetools

[christophebedard]

Description

ros2/rmw_cyclonedds#566 and ros2/rmw_fastrtps#868 added the rmw_take tracepoint to the loaned message take functions.

We should add a test for this to test_tracetools. It would be very similar to test_pub_sub.py but with loaned messages. We specifically want to check that there is a rmw_take trace event for the loaned message received/taken by the subscription node.

Motivation

Better test coverage == better code

Design / Implementation Considerations

Implement test first, then try running the test without the tracepoints from the PRs mentioned above. The test should fail, indicating that the test nodes indeed do use loaned messages. Otherwise the nodes might incorrectly use normal/non-loaned messages and we might never find out.

Additional Information

No response

[christophebedard]

@nightduck could you comment here so that I can assign you? Otherwise it won't let me assign you

[nightduck]

dibs