Move rkyv RPC support to use CRC32 checksums rather than checkbytes and use stack allocated scratch.

[ChillFish8]

This should improve the performance on smaller message payloads by cutting out lots of small allocations on the serializer side when messages require less than 1KB of scratch space.

• We also move to checksum-based validation to ensure better data integrity not just layout and alignment.
• DataView has also had its D (data holder) generic removed as it is completely unnecessary.
• This allows users to use the RPC system without needing check bytes.