Function run_batch 

pub fn run_batch(
    plan: &Plan,
    source: &dyn InputSource,
    ids: &[String],
    store: &dyn ArtifactStore,
    workers: usize,
    on_done: &(dyn Fn(&RecordingRun) + Sync),
) -> Result<Vec<RecordingRun>, PipelineError>

Runs a plan once per recording, workers recordings at a time (0 = all cores). on_done sees each recording as soon as it finishes, for progress or saving.