Add partial rkyv support + parallel qbvh traversal + Heigthfield support of Cuda kernels

[sebcrozet]

Added

• Add the support of Heightfields on CUDA kernels written in Rust using the cust crate.
• Add the rkyv-serialize feature that enables the implementation of rkyv serialization/deserialization
  for most shapes.
• Add the parallel feature that enables methods for the parallel traversal of QBVH trees: QBVH::traverse_bvtt_parallel,
  QBVH::traverse_bvtt_node_parallel, QBVH::traverse_depth_first_parallel, QBVH::traverse_depth_first_node_parallel,