feat: implement lazy loading of members in NamedSelection to speed up loading times when reading model

[RobPasMue]

Description

This issue resolves the large loading times when reading designs - caused by the existence of NamedSelections and the whole in-place loading that was taking place. Reading all its members is not necessary unless requested.

Issue linked

Closes #1863

Checklist

• I have tested my changes locally.
• I have added necessary documentation or updated existing documentation.
• I have followed the coding style guidelines of this project.
• I have added appropriate unit tests.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have added the minimum version decorator to any new backend method implemented.
• I have made sure that the title of my PR follows Conventional commits style (e.g. feat: extrude circle to cylinder)

[codecov]

Codecov Report

Attention: Patch coverage is 89.74359% with 4 lines in your changes missing coverage. Please review.

Project coverage is 90.18%. Comparing base (b8d0e35) to head (1828277).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ansys/geometry/core/designer/selection.py	88.88%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1869      +/-   ##
==========================================
- Coverage   90.21%   90.18%   -0.03%     
==========================================
  Files          92       92              
  Lines        8837     8852      +15     
==========================================
+ Hits         7972     7983      +11     
- Misses        865      869       +4     

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