Interface MeshBvhBuilderConfig

Move the input buffers into the worker instead of copying them. The caller's arrays become unusable (empty) afterwards. Off by default.

'auto' (default) uses a worker when Worker exists, and builds on the calling thread if it can't start or load (no build is lost). 'never' always builds inline; 'always' throws when there is no Worker and rejects the builds when the worker can't start or load.