`cddl-derive` literals and ranges aren't emitted

Literals and ranges aren't emitted in the Rust codegen using `cddl-derive`.

Repro:
```cddl
color = "red"
scale = 1..10

container = {
  name: color,
  level: scale,
}
```
Errors:
- ```cannot find type `Scale` in this scope```
- ```cannot find type `Color` in this scope```