Segmenting nested reads

How should we segment nested reads?

For example, in the current generator:
```cs
yield return SyntaxFactory.ParseStatement($"{outputName}.{field.Name} = {fieldType.Name}.FromBinary(reader);");
```

This can neither be a fixed or a dynamic segment. The idea is to recursively build segments for the type and then commit a `ObjectSegment` detailing if its fixed or dynamic based on the fields inside.