Add batch price retrieval for products in region

- Implemented a new endpoint to fetch prices for multiple products in a specified region in a single request, improving efficiency.
- Added validation for input parameters to ensure proper data handling.
- Updated the FalukantService to calculate prices based on knowledge factors and worth percentages for each product.
- Modified the frontend to utilize the new batch endpoint, optimizing the loading of product prices.

backend/routers/falukantRouter.js

@@ -76,6 +76,7 @@ router.get('/politics/open', falukantController.getOpenPolitics);
 router.post('/politics/open', falukantController.applyForElections);
 router.get('/cities', falukantController.getRegions);
 router.get('/products/price-in-region', falukantController.getProductPriceInRegion);
+router.get('/products/prices-in-region-batch', falukantController.getProductPricesInRegionBatch);
 router.get('/products/prices-in-cities', falukantController.getProductPricesInCities);
 router.get('/branches/:branchId/taxes', falukantController.getBranchTaxes);
 router.get('/vehicles/types', falukantController.getVehicleTypes);