BoundingBox helper: add batch methods

[Popov72]

You can now do:

await BBHelper.batchInitializeAsync(meshList);
BBHelper.batchProcess();
<...update animation...>
BBHelper.batchProcess();
<...update animation...>
BBHelper.batchProcess();
...
await BBHelper.batchFetchResultsAsync();

This will calculate bounding boxes that are the union of all the bounding boxes computed by each call to batchProcess.

The existing API (computeAsync) still exists, this PR is not a breaking change.

Note: I'm not sure if the new methods have the right name...

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s). To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s). To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

Snapshot stored with reference name: refs/pull/15225/merge

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[bjsplat]

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[bjsplat]

Visualization tests for WebGPU (Experimental)

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