docs: public Cursor<T> openCursor(final Txn<T> txn) {
      if (SHOULD_CHECK) {
        requireNonNull(txn);
        txn.checkReady();
      }
      final PointerByReference cursorPtr = new PointerByReference();
      checkRc(LIB.mdb_cursor_open(txn.pointer(), ptr, cursorPtr));
      return new Cursor<>(cursorPtr.getValue(), txn);
    }