Function gen_method 

pub fn gen_method(
    method: &MethodDef,
    mapper: &dyn TypeMapper,
    cfg: &RustBindingConfig<'_>,
    typ: &TypeDef,
    is_opaque: bool,
    opaque_types: &AHashSet<String>,
    adapter_bodies: &AdapterBodies,
) -> String

Generate an instance method.

When is_opaque is true, generates delegation to self.inner via Arc clone instead of converting self to core type.

opaque_types is the set of opaque type names, used for correct return wrapping.