[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/src/css/base/variables.css

@@ -16,26 +16,27 @@
     --info-color: #17a2b8;
     --light-color: #f8f9fa;
     --dark-color: #2d3748;
-    
+
     /* Text colors */
     --text-primary: #1a202c;
     --text-secondary: #4a5568;
     --text-muted: #6b7280;
-    
+
     /* Border colors */
     --border-light: #e2e8f0;
     --border-medium: #cbd5e0;
     --border-dark: #718096;
-    
+
     /* ========== TYPOGRAPHY ========== */
-    --font-family-base: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
+    --font-family-base: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
+        Arial, sans-serif;
     --font-weight-light: 300;
     --font-weight-normal: 400;
     --font-weight-medium: 500;
     --font-weight-semibold: 600;
     --font-weight-bold: 700;
     --font-weight-extrabold: 800;
-    
+
     /* ========== SPACING ========== */
     --spacing-xs: 0.25rem;
     --spacing-sm: 0.5rem;
@@ -43,23 +44,23 @@
     --spacing-lg: 1.5rem;
     --spacing-xl: 2rem;
     --spacing-2xl: 3rem;
-    
+
     /* ========== BORDER RADIUS ========== */
     --radius-sm: 0.25rem;
     --radius-md: 0.5rem;
     --radius-lg: 0.75rem;
     --radius-xl: 1rem;
-    
+
     /* ========== SHADOWS ========== */
     --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.08);
     --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
     --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.12);
-    
+
     /* ========== TRANSITIONS ========== */
     --transition-fast: 200ms ease;
-    --transition-normal: 320ms cubic-bezier(.2, .9, .2, 1);
+    --transition-normal: 320ms cubic-bezier(0.2, 0.9, 0.2, 1);
     --transition-slow: 500ms ease;
-    
+
     /* ========== Z-INDEX ========== */
     --z-dropdown: 1000;
     --z-sticky: 1020;