feat(promo): Enhance promo code functionality and discount consumption logic

- Integrated promo code service into subscription service to streamline discount consumption during payment processing.
- Improved error handling and logging for promo code activation and usage increment.
- Updated payment services to handle discount calculations more robustly, including fallback mechanisms for invalid discount scenarios.
- Added new methods for managing promo code activations and usage in the database layer.

bot/handlers/user/promo_user.py

@@ -190,9 +190,10 @@ async def process_promo_code_input(message: types.Message, state: FSMContext,
                 # Both failed
                 await session.rollback()
                 logging.info(
-                    f"Promo code '{code_input}' application failed for user {user.id}. Reason: {result}"
+                    f"Promo code '{code_input}' application failed for user {user.id}. "
+                    f"Bonus reason: {result}. Discount reason: {result_discount}"
                 )
-                response_to_user_text = result  # Original error message from bonus code attempt
+                response_to_user_text = result_discount  # Prefer the discount attempt error
                 reply_markup = get_back_to_main_menu_markup(
                     current_lang, i18n
                 )