This adds South Africa localization so businesses can use a ready-made chart of accounts, tax setup, and related accounting templates in Odoo. It helps South African companies start accounting operations faster and improves compatibility with Odoo Enterprise.

Description of the issue/feature this PR addresses:
Potential localization for South Africa issue #22873 

Current behavior before PR:
No localization available

Desired behavior after PR is merged:

Localization works and is compatible with odoo enterprise


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Users can now download Odoo spreadsheets in an Excel-compatible .xlsx format, making it easier to share and work with files outside Odoo. The update also ensures month and quarter filters keep a default year, preventing unclear filter results in spreadsheets.

Users can now download Odoo spreadsheets as Excel-compatible .xlsx files, making it easier to share and work with spreadsheet data outside Odoo. The update also improves date filter handling and cleans sheet names during export to avoid Excel compatibility issues.

Odoo task ID: [2291419](https://www.odoo.com/web#action=327&cids=1&id=2291419&menu_id=4720&model=project.task&view_type=form)