Long term references are not kept long term.

@alexismt reported here https://github.com/AOMediaCodec/av2-spec-internal/issues/742#issuecomment-3965063438 that the design intention of long term references was:

that the OLK process should not reset any slots with long term reference frames.

However, the code does not implement this:

  static void reset_buffer_other_than_OLK(AV2Decoder *pbi) {
  AV2_COMMON *const cm = &pbi->common;
  const SequenceHeader *const seq_params = &cm->seq_params;
  BufferPool *const pool = cm->buffer_pool;
  int ref_flags_to_keep = 0;
  for (int layer = 0; layer <= seq_params->max_mlayer_id; layer++) {
    if (cm->olk_refresh_frame_flags[layer] == -1) continue;
    ref_flags_to_keep |= cm->olk_refresh_frame_flags[layer];
  }
  for (int ref_index = 0; ref_index < seq_params->ref_frames; ref_index++) {
    if (!((ref_flags_to_keep >> ref_index) & 1u)) {
      decrease_ref_count(cm->ref_frame_map[ref_index], pool);
      cm->ref_frame_map[ref_index] = NULL;
      if (pbi->random_accessed) pbi->valid_for_referencing[ref_index] = 1;
    }
  }
}

Note that there is no code to keep long term references around.