test: shut rclcpp down after every lifecycle handler suite

[bburda]

Summary

test_lifecycle_handlers could exit with SIGSEGV after every test passed. Two of its three fixtures had an empty TearDownTestSuite, so the default context was still initialised when the process left main. rclcpp 28.1.22 shuts that context down from a static destructor inside exit(), which runs after the main thread's thread_local objects are destroyed, and Context::shutdown touches one of them. The crash needs an earlier main-thread shutdown to have created that object, and LifecycleHandlersTest does that in its own teardown.

Both fixtures now shut rclcpp down the same guarded way as the first one. Every SetUpTestSuite in the file already guards on rclcpp::ok(), so a later suite re-initialises safely.

Ten other test sources call rclcpp::init and never rclcpp::shutdown. None of them shuts a context down on the main thread, and a program that only initialises never crashes this way, so they are left as they are.

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Issue

• none, test-only change

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Type

• Bug fix
• New feature or tests
• Breaking change
• Documentation only

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Testing

In a container on ros:jazzy-ros-base (rclcpp 28.1.22; the development machine has 28.1.21, where the crash cannot happen), running the real binary with one test per fixture so the exit shape is kept:

• before: 54 runs, 9 segfaults, each with all tests passed;
• after: 200 runs, 0 segfaults, and 5 of 5 full runs of the unfiltered suite exit 0.

Four minimal rclcpp programs, 50 runs each, show the shape: init only and init plus shutdown are clean, init plus shutdown plus init segfaults in 10 of 50, and init plus shutdown plus init plus shutdown is clean. The backtrace is Context::shutdown under ~Context under __run_exit_handlers.

colcon test --packages-select ros2_medkit_gateway: 4306 tests, 0 failures.

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Checklist

• Breaking changes are clearly described (and announced in docs / changelog if needed)
• Tests were added or updated if needed
• Docs were updated if behavior or public API changed