Behavior before:
When exporting the VAT report to XML, each newly added line triggered a fresh _compute_expression_totals_for_each_column_group call. With large volumes of journal items, this resulted in excessive repeated queries and, for big datasets, timeout errors.

Behavior after:
Introduced _custom_unfold_all_batch_data_generator, which batches the computation of expression totals for all lines. Now, journal items are resolved in bulk and mapped back to their respective moves, significantly reducing redundant queries. The VAT XML export completes successfully, even on months with very large datasets.

Root cause:
The Estonia VAT report was missing a batch unfold method (_custom_unfold_all_batch_data_generator). Without it, the system executed totals computation for each line individually instead of in batch, causing major performance degradation.

Benchmark:

| Period size (journal items)  | Before patch   | After patch   |
|----------------------------------------|----------------------|--------------------|
| ~15k                                        | 7s                      | 5s                   |
| ~200k+                                    | Timeout error| 21s                 |


opw-5046077