Function warn_on_unparseable_events 

fn warn_on_unparseable_events(events_jsonl: &str)

Events are checked leniently: a line we can’t parse — e.g. an event type written by a newer Entracte — must not brick the whole import. The events file is written verbatim and the stats reader (crate::stats::read_all) already drops lines it can’t parse, so unknown events are preserved on disk and simply ignored when computing stats. We only count and warn so the drop isn’t silent — matching the runtime reader’s tolerance rather than the old all-or-nothing reject.