Add cashier name retrieval and caching logic to orders processing

- Introduced `getCashierName` method in `users_o` for cashier name retrieval.
- Added caching for cashier names with dedicated expiration settings.
- Updated `ordersRoute` to include cashier names in order details.
- Added `$cashierNameCacheExpiration` property in `db_object_t` for centralized cache control.

services/nginx/app/objects/users_o.php

@@ -1461,4 +1461,28 @@ class users_o extends db
         return $customer_names;
     }
 
+    public function getCashierName(int $cashier_id): string
+    {
+        $virtualCacheObjectID = "cashier_$cashier_id";
+        $cache_key = 'cashier_name';
+        // Check if the name is cached
+        $cached_name = $this->getCached($cache_key, $virtualCacheObjectID);
+        if ($cached_name) {
+            return (string)$cached_name;
+        } else {
+            // Not cached, get the name from the database
+            $cashier = new users_o();
+            $cashier->select($cashier_id);
+            $name = $cashier->display_name->value();
+            // If the name is empty, set it to 'Unknown Cashier'
+            if (empty($name)) {
+                $name = 'Unknown Cashier';
+            }
+            // Cache the name
+            $this->cache($cache_key, $name, $virtualCacheObjectID);
+            $this->setCachedExpiration($cache_key, self::$cashierNameCacheExpiration, $virtualCacheObjectID);
+            return $name;
+        }
+    }
+
 }