Enable RMW isolation for single process tests

[Yadunund]

Description

#960 enabled RMW isolation for test_tf2 launch tests but not single process tests that call rclcpp::init / rclpy.init.

When testing with rmw_zenoh, those still connect to default tcp/localhost:7447 with an infinite peer connect timeout, so session open can hang and ctest reports gtest.missing_result.

That showed up as an intermittent zenoh nightly failure: 119 passed, 120 failed on test_message_filter with no source changes.

This PR wraps remaining ROS-init tests with the fixture:

• test_tf2 / tf2_ros: ament_add_ros_isolated_gtest for gtests that call rclcpp::init
• tf2_ros_py: session-scoped conftest.py (ament_python has no CMake isolated runner)

Fixes # (issue)

Is this user-facing behavior change?

No

Did you use Generative AI?

Yes. Cursor (Grok 4.6) for diagnosis and the isolation wiring.

Additional Information

Launch isolation from #960 is unchanged.

[cottsay]

Changes look good.

[Yadunund]

CI started with: https://gist.githubusercontent.com/Yadunund/62882e88df23c7375068cc6bcad1691d/raw/e14b9f51eb6be6e070459a7888889a8953540e85/ros2.repos
BUILD_ARGS: --packages-up-to tf2_ros test_tf2 tf2_ros_py
TEST_ARGS: --packages-select tf2_ros test_tf2 tf2_ros_py
Launcher: https://ci.ros2.org/job/ci_launcher/20315/

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[ahcorde]

https://github.com/Mergifyio backport lyrical

[mergify]

backport lyrical

✅ Backports have been created

Details

• #985 Enable RMW isolation for single process tests (backport #983) has been created for branch lyrical but encountered conflicts

Cherry-pick of bcee5a2 has failed:

On branch mergify/bp/lyrical/pr-983
Your branch is up to date with 'origin/lyrical'.

You are currently cherry-picking commit bcee5a2.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   tf2_ros/CMakeLists.txt
	modified:   tf2_ros/package.xml
	new file:   tf2_ros_py/conftest.py
	modified:   tf2_ros_py/package.xml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   test_tf2/CMakeLists.txt
	both modified:   test_tf2/package.xml

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