Variable LBVH_STAGES`Const`

LBVH_STAGES: readonly [
    "boxes",
    "morton",
    "sort",
    "clear",
    "climb",
    "mark",
    "rank",
    "triangles",
    "emit",
] = ...

The steps of a batch's build, in order, as GpuLbvhBatch.encode can time them.