Adding tests for hydrodynamics

[quarkytale]

Summary

Ball drop test

Test it

Run all tests colcon test --event-handlers console_direct+ --packages-select gz-sim7 or the test world directly gz sim src/ign-gazebo/test/worlds/hydrodynamics.sdf

Checklist

• [x] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [x] Consider updating Python bindings (if the library has them)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [x] While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.