feat(model): move model loading into worker

[fallenoak]

This PR introduces an alternative SceneWorker implementation (expected to be bundled, not inlined), and sets up a ModelLoader built on top of SceneWorker to shift model loading off the main thread. Heavy model data like the vertex buffer and index buffer is flagged as transferable to avoid copies.

[codecov-commenter]

Codecov Report

Attention: 179 lines in your changes are missing coverage. Please review.

Comparison is base (fac62a2) 14.59% compared to head (1fa411a) 13.36%.

Files	Patch %	Lines
src/lib/model/loader/ModelLoaderWorker.ts	0.00%	42 Missing and 2 partials ⚠️
src/lib/worker/SceneWorker.ts	0.00%	26 Missing and 6 partials ⚠️
src/lib/model/loader/util.ts	0.00%	16 Missing and 6 partials ⚠️
src/lib/worker/SceneWorkerController.ts	0.00%	18 Missing and 1 partial ⚠️
src/lib/model/ModelManager.ts	0.00%	14 Missing and 3 partials ⚠️
src/lib/model/types.ts	0.00%	11 Missing and 2 partials ⚠️
src/lib/model/shader/vertex.ts	0.00%	4 Missing and 4 partials ⚠️
src/lib/model/loader/ModelLoader.ts	0.00%	6 Missing ⚠️
src/lib/model/shader/fragment.ts	0.00%	3 Missing and 3 partials ⚠️
src/lib/AssetManager.ts	0.00%	4 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #30      +/-   ##
==========================================
- Coverage   14.59%   13.36%   -1.23%     
==========================================
  Files          33       41       +8     
  Lines        1357     1481     +124     
  Branches      253      272      +19     
==========================================
  Hits          198      198              
- Misses       1013     1118     +105     
- Partials      146      165      +19     

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