refactor: extract Brent price sources into dedicated classes

OilPriceService no longer inlines per-provider fetch/transform/error logic.
EIA and FRED are now their own classes with a common shape; the service
just iterates and upserts the first successful result.

tests/Unit/Services/OilPriceServiceTest.php

@@ -5,6 +5,8 @@ use App\Enums\TrendDirection;
 use App\Models\BrentPrice;
 use App\Models\PricePrediction;
 use App\Services\ApiLogger;
+use App\Services\BrentPriceSources\EiaBrentPriceSource;
+use App\Services\BrentPriceSources\FredBrentPriceSource;
 use App\Services\LlmPrediction\OilPredictionProvider;
 use App\Services\OilPriceService;
 use Illuminate\Foundation\Testing\RefreshDatabase;
@@ -15,7 +17,12 @@ uses(RefreshDatabase::class);
 beforeEach(function (): void {
     Http::preventStrayRequests();
     $this->provider = Mockery::mock(OilPredictionProvider::class);
-    $this->service = new OilPriceService(new ApiLogger, $this->provider);
+    $apiLogger = new ApiLogger;
+    $this->service = new OilPriceService(
+        $this->provider,
+        new EiaBrentPriceSource($apiLogger),
+        new FredBrentPriceSource($apiLogger),
+    );
 });
 
 // --- fetchBrentPrices ---