feat: FuelPriceService with OAuth token caching

Also extend Pest TestCase to Unit tests and guard MySQL-only migration
DDL (composite PK + PARTITION BY) behind a driver check so in-memory
SQLite tests can run migrations cleanly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/Pest.php

@@ -16,7 +16,7 @@ use Tests\TestCase;
 
 pest()->extend(TestCase::class)
  // ->use(RefreshDatabase::class)
-    ->in('Feature');
+    ->in('Feature', 'Unit');
 
 /*
 |--------------------------------------------------------------------------