Macro impl_packed_value 

macro_rules! impl_packed_value {
    ($alg_type:ty, $field_type:ty, $width:expr $(, ($type_param:ty, $param_name:ty))?) => { ... };
}

Given Field and Algebra structs where Algebra is simply a wrapper around [Field; N] implement PackedValue for Algebra.

Safety

Algebra must be repr(transparent) and castable from to/from [Field; N]. Assuming this holds, these types have the same alignment and size, so all our reference casts are safe.