Refactor magnetometer demo

[caguero]

Refactors the magnetomer demo leveraging the latest improvements in ros_gz.

• I replaced the previous launch file from Python to XML.

Summary

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• 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.

[ahcorde]

I can't see the values in rqt_topic

[caguero]

I can't see the values in rqt_topic

Are you expanding the topic? It works for me...

[ahcorde]

LGTM, but I can see this trace

[component_container-1] (2024-12-13 16:33:46.234) [warning] [Magnetometer.cc:462] Failed to update Magnetometer sensor enity [16]. Spherical coordinates not set.
[component_container-1] (2024-12-13 16:33:46.234) [warning] [Magnetometer.cc:462] Failed to update Magnetometer sensor enity [16]. Spherical coordinates not set.
[component_container-1] (2024-12-13 16:33:46.234) [warning] [Magnetometer.cc:462] Failed to update Magnetometer sensor enity [16]. Spherical coordinates not set.
[component_container-1] (2024-12-13 16:33:46.234) [warning] [Magnetometer.cc:462] Failed to update Magnetometer sensor enity [16]. Spherical coordinates not set.
...