dev: add trading pairs request

src/Requests/GetTradingPairsRequestContract.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Msr\LaravelBitunixApi\Requests;
+
+use Psr\Http\Message\ResponseInterface;
+
+interface GetTradingPairsRequestContract
+{
+    /**
+     * Get future trading pair details
+     *
+     * @param string|null $symbols Trading pairs, comma-separated (e.g., "BTCUSDT,ETHUSDT,XRPUSDT")
+     * @return ResponseInterface
+     */
+    public function getTradingPairs(?string $symbols = null): ResponseInterface;
+}
+