Normalize stdClass to array in Request::fromArray() for param type safety

Converts stdClass to an associative array when decoding 'params' in JsonRpc\Request,
ensuring type compliance with downstream DTOs.

Fixes php-mcp/server#53
See php-mcp/server#53 (comment)

Author: judus

src/JsonRpc/Request.php

@@ -42,6 +42,9 @@ public static function fromArray(array $data): static
             throw new \InvalidArgumentException('Invalid or missing "method" for Request.');
         }
         $params = $data['params'] ?? null;
+        if ($params instanceof \stdClass) {
+            $params = (array) $params;
+        }
         if ($params !== null && !is_array($params)) {
             throw new \InvalidArgumentException('"params" for Request must be an array/object or null.');
         }