Having a struct with generics like this
```rust
pub struct Signature<T: PrimeCurve>
where
    SignatureSize<T>: ArrayLength<u8>,
{
    signature: ecdsa::Signature<T>,
}
```

Is there any way to express the same two bounds on the generic in a trait GAT? 
```rust
trait Foo {
    type Curve: PrimeCurve; // How to add where SignatureSize<T>: ArrayLength<u8>?
}
```