Refactor exchange rate providers into driver-based architecture

Replace duplicated switch/case blocks across 4 methods with a clean
abstract driver pattern:

- ExchangeRateDriver (abstract): defines getExchangeRate(),
  getSupportedCurrencies(), validateConnection()
- CurrencyFreakDriver, CurrencyLayerDriver, OpenExchangeRateDriver,
  CurrencyConverterDriver: concrete implementations
- ExchangeRateDriverFactory: resolves driver name to class, with
  register() method for module extensibility

Delete ExchangeRateProvidersTrait — all logic now lives in driver
classes and ExchangeRateProviderService. Adding a new exchange rate
provider only requires implementing ExchangeRateDriver and calling
ExchangeRateDriverFactory::register() in a module service provider.

app/Services/ExchangeRate/CurrencyConverterDriver.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace App\Services\ExchangeRate;
+
+use Illuminate\Support\Facades\Http;
+
+class CurrencyConverterDriver extends ExchangeRateDriver
+{
+    public function getExchangeRate(string $baseCurrency, string $targetCurrency): array
+    {
+        $baseUrl = $this->getBaseUrl();
+        $query = "{$baseCurrency}_{$targetCurrency}";
+        $url = "{$baseUrl}/api/v7/convert?apiKey={$this->apiKey}&q={$query}&compact=y";
+        $response = Http::get($url)->json();
+
+        return array_values($response[$query]);
+    }
+
+    public function getSupportedCurrencies(): array
+    {
+        $baseUrl = $this->getBaseUrl();
+        $url = "{$baseUrl}/api/v7/currencies?apiKey={$this->apiKey}";
+        $response = Http::get($url)->json();
+
+        if ($response == null) {
+            throw new ExchangeRateException('Server not responding', 'server_error');
+        }
+
+        if (array_key_exists('results', $response)) {
+            return array_keys($response['results']);
+        }
+
+        throw new ExchangeRateException('Please Enter Valid Provider Key.', 'invalid_key');
+    }
+
+    public function validateConnection(): array
+    {
+        $baseUrl = $this->getBaseUrl();
+        $query = 'INR_USD';
+        $url = "{$baseUrl}/api/v7/convert?apiKey={$this->apiKey}&q={$query}&compact=y";
+        $response = Http::get($url)->json();
+
+        return array_values($response[$query]);
+    }
+
+    private function getBaseUrl(): string
+    {
+        $type = $this->config['type'] ?? 'FREE';
+
+        return match ($type) {
+            'PREMIUM' => 'https://api.currconv.com',
+            'PREPAID' => 'https://prepaid.currconv.com',
+            'FREE' => 'https://free.currconv.com',
+            'DEDICATED' => $this->config['url'] ?? 'https://free.currconv.com',
+        };
+    }
+}