Initialize the namespace property for custom iMarkers in rviz (backport #3547)

[mergify]

Description

MoveIt's iMarker doesn't initialize the marker namespace property, so that functionality is broken when you try to add other iMarkers alongside moveit's planning interface. Normally this just breaks the cursor, though in some cases we've seen rviz crash. I was under the impression that pluginlib might still load the default plugin for other markers, but that does not seem to be the case.

Regardless, I don't think there's a downside to providing the node abstraction to the namespace property object, so this PR just uncomments those lines.

Before (cursor gets stuck as a spinning wheel):

Screen.Recording.2025-08-09.at.10.47.21.AM.mov

After:

Screen.Recording.2025-08-09.at.10.49.49.AM.mov

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

---

This is an automatic backport of pull request #3547 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.20%. Comparing base (e489b04) to head (0569a49).
⚠️ Report is 1 commits behind head on jazzy.

Files with missing lines	Patch %	Lines
...ing_rviz_plugin/src/interactive_marker_display.cpp	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            jazzy    #3551      +/-   ##
==========================================
- Coverage   46.21%   46.20%   -0.00%     
==========================================
  Files         718      718              
  Lines       62675    62679       +4     
  Branches     7589     7590       +1     
==========================================
- Hits        28957    28953       -4     
- Misses      33554    33559       +5     
- Partials      164      167       +3     

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[github-actions]

This PR is stale because it has been open for 45 days with no activity. Please tag a maintainer for help on completing this PR, or close it if you think it has become obsolete.