### Issue -->

The final step of the `_action_merge` method updates the `code` field of the account onto which the other accounts are merged. During the write call on `code`, a dependent field `always_tax_exigible` on `account.move` gets added to the compute chain. This causes a fetch of all `account.move` records related to journal items related to the account that is getting updated. This can lead to a MemoryError on databases with large `account.move` tables.

### Solution -->

We delegate the write of the `code` field to SQL.

In the account merge wizard, accounts that can be grouped are grouped by the keys --> `'account_type', 'non_trade', 'currency_id', 'reconcile', 'deprecated','name'`. Therefore, the `account_type` does not change after the merge. We can safely assume that any fields dependent on `account_type` do not need recomputation and hence, bypass the ORM for this update.

### Benchmark -->
For an account with ~1.17M related `account_move_lines` and ~570k `account_moves`, 

| Before Fix | After Fix |
|--------|--------|
| TO/Memory error past TO | ~24s | 


#### Additional change -->

Disable the prefetcher in the write call in `account.account` to optimize memory usage on databases with a large number of journal items/journal entries when writing on `code` or `account_type` in general.

opw-4839985

Forward-Port-Of: odoo/odoo#216768