fix: generate async delegate methods
Fixes a bug where the generated async method doesn't await the result before returning it.
This is an example of what the output looked like:
```rust
struct Age<T>(T);
impl<T> Age<T> {
pub(crate) async fn age<J, 'a>(&'a mut self, ty: T, arg: J) -> T {
self.0
}
}
struct Person<T> {
age: Age<T>,
}
impl<T> Person<T> {
pub(crate) async fn age<J, 'a>(&'a mut self, ty: T, arg: J) -> T {
self.age.age(ty, arg) // .await is missing
}
}
```
The `.await` is missing, so the return type is `impl Future<Output = T>` instead of `T`
b0214d81e8