Native-only build does not process examples

[subversive-owl]

This is maybe caused by missing backend implementations, but if a native build is created it returns immediately when models are run.

Build with: cargo build --no-default-features --features="native" --release

Run any model, e.g.: target/release/juice-examples mnist linear --batch-size 20

Returns almost immediately with no results printed.

[drahnr]

Right now this is not implemented, this is more of a TODO