Macro part_codec 

macro_rules! part_codec {
    (
        impl <$($impl_generics:ident),+> $ty:ty
        {
            type Repr = $repr:ty;
        }
    ) => { ... };
    (
        impl $ty:ty
        {
            type Repr = $repr:ty;
        }
    ) => { ... };
    (
        @expand
        [$($impl_generics:tt)*]
        [$($de_impl_generics:tt)*]
        [$ty:ty]
        [$repr:ty]
    ) => { ... };
}

Implement PartCodec, serde::Serialize, and serde::Deserialize.