refactor: extract rate formatting logic to RateService and add tests

database/seeders/DatabaseSeeder.php

@@ -16,18 +16,13 @@ class DatabaseSeeder extends Seeder
     public function run(): void
     {
         // currencies
-        $saudiRial = Currency::factory()->saudiRial()->create();
         $usdDollar = Currency::factory()->usdDollar()->create();
+        $saudiRial = Currency::factory()->saudiRial()->create();
 
         // cities
         $sanaa = City::factory()->sanaa()->create();
         $aden = City::factory()->aden()->create();
 
-        // rates
-        Rate::factory()->recycle($usdDollar)->recycle($sanaa)->create();
-        Rate::factory()->recycle($usdDollar)->recycle($aden)->create();
-
-        Rate::factory()->recycle($saudiRial)->recycle($sanaa)->create();
-        Rate::factory()->recycle($saudiRial)->recycle($aden)->create();
+        // we will seed rates with commands instead
     }
 }