Add support for scene hierarchy USD importer

[Medyan-Naser]

Describe your changes

• Add scene hierarchy support for USD importer: Implemented GetOrCreateHierarchyNode() method to build a proper vtkDataAssembly hierarchy from USD scene structure
• Enhanced USD test coverage: Added unit test verification for scene hierarchy nodes and actor attributes

Issue ticket number and link if any

closes #2950

Checklist for finalizing the PR

• I have performed a self-review of my code
• I have added tests for new features and bugfixes
• I have added documentation for new features
• If it is a modifying the libf3d API, I have updated bindings
• If it is a modifying the .github/workflows/versions.json, I have updated docker_timestamp

Continuous integration

Please write a comment to run CI, eg: \ci fast.
See here for more info.

[Medyan-Naser]

@mwestphal
Please review my changes.

[mwestphal]

changes needed

[mwestphal]

\ci fast

[mwestphal]

LGTM but I defer to @Meakk

[Meakk]

LGTM, please fix the style and we'll merge it

[codecov]

Codecov Report

❌ Patch coverage is 97.43590% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 97.13%. Comparing base (52eabba) to head (5a74a03).

Files with missing lines	Patch %	Lines
plugins/usd/module/vtkF3DUSDImporter.cxx	97.43%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2954      +/-   ##
==========================================
- Coverage   97.14%   97.13%   -0.01%     
==========================================
  Files         206      206              
  Lines       16508    16535      +27     
==========================================
+ Hits        16036    16062      +26     
- Misses        472      473       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Meakk]

Please check why the coverage misses a line. The test is also failing with VTK 9.3, add a CMake condition like other scene hierarchy tests

[Medyan-Naser]

Please check why the coverage misses a line. The test is also failing with VTK 9.3, add a CMake condition like other scene hierarchy tests

Regarding the coverage gap on line 165: this corresponds to return it->second;, which is the cache-hit path in GetOrCreateHierarchyNode. This branch is only exercised when the same USD path is queried more than once.