[#310] Added classmethod decorator in Http client

Signed-off-by: Dmitriy Zayakin <d.zayakin@yadro.com>

src/frostfs_testlib/http/http_client.py

@@ -50,6 +50,7 @@ class HttpClient:
 
         return response
 
+    @classmethod
     def _attach_response(self, response: httpx.Response):
         request = response.request
 
@@ -88,6 +89,7 @@ class HttpClient:
         reporter.attach(report, "Requests Info")
         reporter.attach(curl_request, "CURL")
 
+    @classmethod
     def _create_curl_request(self, url: str, method: str, headers: httpx.Headers, data: str) -> str:
         headers = " ".join(f'-H "{name.title()}: {value}"' for name, value in headers.items())
         data = f" -d '{data}'" if data else ""