`GodotConvert` derive-macro and `godot(transparent)` with `PhantomData`

It should be possible to derive `GodotConvert` with `godot(transparent)` on structs that have `PhantomData` and generics.

For example:

```rs
#[derive(GodotConvert)]
#[godot(transparent)]
pub struct Id(u32, PhantomData);
```

This struct is basically a newtype around `u32` with some extra rust typing, and so it makes sense that this should be representable in Godot.

Start at the GodotConvert derive macro and inspect how godot(transparent) handles generic structs and PhantomData. Use the Id example from the issue as the reproduction case; the work is done when this declaration derives successfully and represents the u32 value in Godot.

Written by the indexing model from the issue text.