tests: use AES-GCM key generation

src/tests/test_nostr_contract.py

@@ -3,7 +3,8 @@ from pathlib import Path
 from unittest.mock import patch
 import asyncio
 import gzip
-from cryptography.fernet import Fernet
+import os
+import base64
 
 sys.path.append(str(Path(__file__).resolve().parents[1]))
 
@@ -61,7 +62,7 @@ class MockClient:
 
 
 def setup_client(tmp_path, server):
-    key = Fernet.generate_key()
+    key = base64.urlsafe_b64encode(os.urandom(32))
     enc_mgr = EncryptionManager(key, tmp_path)
 
     with patch("nostr.client.Client", lambda signer: MockClient(server)), patch(