Spreadsheet currency rate lookups now use the same date logic as currency rates created by users, including the creator's time zone. This helps prevent incorrect exchange rates from being used around date boundaries, improving accuracy for financial reporting.

The defaut `name` (which is a Date) of a `res.currency.rate` is computed
based on its creator's TZ. The look up of currency rates in spreadsheet
should follow the same logic.

Task 2869705