[FIX] website_sale_aplicoop: Remove redundant string= attributes and fix OCA linting warnings

- Remove redundant string= from 17 field definitions where name matches string value (W8113)
- Convert @staticmethod to instance methods in selection methods for proper self.env._() access
- Fix W8161 (prefer-env-translation) by using self.env._() instead of standalone _()
- Fix W8301/W8115 (translation-not-lazy) by proper placement of % interpolation outside self.env._()
- Remove unused imports of odoo._ from group_order.py and sale_order_extension.py
- All OCA linting warnings in website_sale_aplicoop main models are now resolved

Changes:
- website_sale_aplicoop/models/group_order.py: 21 field definitions cleaned
- website_sale_aplicoop/models/sale_order_extension.py: 5 field definitions cleaned + @staticmethod conversion
- Consistent with OCA standards for addon submission

website_sale_aplicoop/static/tests/README.md

@@ -134,7 +134,7 @@ docker-compose exec odoo odoo -d odoo --test-enable --log-level=test --stop-afte
    odoo.define('website_sale_aplicoop.test_my_feature', function (require) {
        'use strict';
        var QUnit = window.QUnit;
-       
+
        QUnit.module('website_sale_aplicoop.my_feature', {
            beforeEach: function() {
                // Setup code
@@ -257,6 +257,6 @@ exit $exit_code
 
 ---
 
-**Maintainer**: Criptomart  
-**License**: AGPL-3.0  
+**Maintainer**: Criptomart
+**License**: AGPL-3.0
 **Last Updated**: February 3, 2026