Function compute_extra_bounds 

fn compute_extra_bounds(
    methods: &[MethodInfo],
    trait_name: &Ident,
    assoc_types: &[&Ident],
    trait_param_idents: &[&Ident],
) -> ExtraBounds

Compute extra bounds needed for the shim and build_vtable functions.

• Methods returning Self → __ImplT: IntoR
• Methods with &Self params → __ImplT: TypedExternal + Send + 'static
• Methods returning types with Self::AssocType or trait type params → full rewritten return type : IntoR (e.g., Option<<__ImplT as RIterator>::Item>: IntoR)
• Methods with trait type params in params → full param type : TryFromSexp (e.g., Vec<T>: TryFromSexp)