5-task TDD plan: PhysicsDatBundle on LoadedLandblock; worker pre-reads the
apply's six Get<T> sites into it; ApplyLoadedTerrainLocked reads from the
bundle; drop the apply's lock(_datLock); verify lockwait->0; strip probes.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
