Improvement: Fix locking for processing

[felipeblazing]

Currently the way we lock batches for processing (after moving from pin and unpin) is to check if we can lock something for processing, increment a counter, and then require the user to remember to create the handle from this batch. Instead of this try_to_lock_for_processing should return the handle if it works and and an error if it couldn't lock

    if (batch_ptr && batch_ptr->try_to_lock_for_processing()) {
      return {std::move(batch), data_batch_processing_handle{batch_ptr}};
    }