Copy 1 to 200 timeline clips so the earliest copy starts at at_ms and the others keep their offsets from it, each copy on its original's track. All or nothing: an unknown clip id, a clip on a locked track, copies that would run past the timeline cap, a track that would pass its clip cap, or a copy that overlaps any existing clip (the originals included) refuses the whole call, names the first offender, and copies nothing; an overlap refusal gives the nearest at_ms that fits. Returns new_clip_ids in the order the clip_ids were given.