Macro impl_ssd_backend_ext_for_burn_backends 

macro_rules! impl_ssd_backend_ext_for_burn_backends {
    ($trait_name:path) => { ... };
}

Emit impl $trait_name for <backend> {} blocks for every burn backend supported by this crate, opting in to the trait’s default body.

Each impl is feature-gated by the corresponding backend-* / cubecl / fusion feature.