Spaces: Add methods to add/remove space children.

[pixlwave]

• Add SpaceService::add_child_to_space and SpaceService::remove_child_from_space
  • Add tests for adding/removing space children.
• Expose Room::parent_spaces to the FFI
• Public API changes documented in changelogs (optional)

Closes #5821

[codecov]

Codecov Report

❌ Patch coverage is 27.71084% with 60 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.54%. Comparing base (9ab886f) to head (354af15).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-ui/src/spaces/mod.rs	27.71%	60 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5871      +/-   ##
==========================================
- Coverage   88.59%   88.54%   -0.05%     
==========================================
  Files         363      363              
  Lines      102888   102933      +45     
  Branches   102888   102933      +45     
==========================================
- Hits        91153    91142      -11     
- Misses       7496     7550      +54     
- Partials     4239     4241       +2     

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[codspeed-hq]

CodSpeed Performance Report

Merging #5871 will not alter performance

_{Comparing doug/space-children (354af15) with main (9ab886f)}

Summary

✅ 50 untouched