[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/migrations/18.0.1.0.2/post-migrate.py

@@ -1,7 +1,8 @@
 # Copyright 2025 Criptomart
 # License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl)
 
-from odoo import api, SUPERUSER_ID
+from odoo import SUPERUSER_ID
+from odoo import api
 
 
 def migrate(cr, version):
@@ -13,7 +14,7 @@ def migrate(cr, version):
     env = api.Environment(cr, SUPERUSER_ID, {})
 
     # Obtener la compañía por defecto
-    default_company = env['res.company'].search([], limit=1)
+    default_company = env["res.company"].search([], limit=1)
 
     if default_company:
         # Actualizar todos los registros de group.order que no tengan company_id
@@ -23,7 +24,7 @@ def migrate(cr, version):
             SET company_id = %s
             WHERE company_id IS NULL
             """,
-            (default_company.id,)
+            (default_company.id,),
         )
 
         cr.commit()