Function render_batch_parallel 

pub fn render_batch_parallel(
    config: &Config,
    target_for: impl Fn(&Path) -> RenderTarget + Sync,
) -> Result<Vec<(PathBuf, Result<RenderOutput>)>>

Renders every file resolved by config.files() in parallel on a dedicated Rayon thread pool sized by config.num_threads.

Requires the image feature (file decoding via the image crate).