Before
```
expected Token::Str but serialized as Str(“F9168C5E-CEB2-4FAA-B6BF-329BF39FA1E4")
```
After
```
expected Token::Str(“f9168c5e-ceb2-4faa-b6bf-329bf39fa1e4”) but serialized as Str(“F9168C5E-CEB2-4FAA-B6BF-329BF39FA1E4")
```
Since we know exactly how many bytes we should serialize as we can hint
to the serializer that it is not required which further reduces the
serialized size when compared to just serializing as bytes.
This implements the KISS suggested in https://github.com/serde-rs/serde/issues/790.
It is possible that one of the other approaches may be better but this
seemed like the simplest one to reignite som discussion.
Personally I find the original suggestion of adding two traits perhaps slightly
cleaner in theory but I think it ends up more complicated in the end
since the added traits also need to be duplicated to to the `Seed`
traits.
Closes#790