Use the zerocopy library for marshalling/unmarshalling

[kupiakos]

zerocopy is a Rust library designed to enable simple and safe zero-copy serialization and deserialization, aka no-cost marshaling/unmarshaling.

It does this through a set of marker traits:

• AsBytes marks a type as safe to convert to bytes, which means it has no padding or possibly-uninit bytes.
• FromBytes marks a type as valid for every possible initialized bit pattern. Integers, arrays, and #[repr(C)] structs of FromBytes types qualify. The only place this could cause issues is with is with proper enum types, and open-enum aims to help with that.

It also provides derive(FromBytes) and derive(AsBytes), which check that your struct fits the safety conditions and has a stable layout. Through these traits and macros, it defines safe conversions that are mostly out of the way.

I'm working with upstream to improve the library greatly. In particular, the TryFromBytes feature will allow us to define fallible conversions for types that aren't FromBytes and automatically use a verifier function when converting to/from bytes.

[esmusick]

zerocopy is now used underlying all marshaling/unmarshaling with #17 and #24