struct-variant vs zerocopy vs num-conv

Minimal helper macro to generate an enum out of a list of structs.

Zerocopy makes zero-cost memory manipulation effortless. We write "unsafe" so you don't have to.

`num_conv` is a crate to convert between integer types without using `as` casts. This provides better certainty when refactoring, makes the exact behavior of code more explicit, and allows using turbofish syntax.