Function embed_via_backend_strict 

pub fn embed_via_backend_strict(
    models_dir: &Path,
    text: &str,
    backend: &LlmBackendKind,
    last_err: Option<&AppError>,
    skip_on_failure: bool,
) -> Result<(Vec<f32>, LlmBackendKind), AppError>

Embed via backend strict.