refactor(sigv4_helper.py): remove default service string

Author: Kyon Caldera

aws_mcp_proxy/sigv4_helper.py

@@ -186,7 +186,7 @@ def create_sigv4_auth(
 
 
 def create_sigv4_client(
-    service: str = 'your-service',
+    service: str = '',
     profile: Optional[str] = None,
     region: Optional[str] = None,
     headers: Optional[Dict[str, str]] = None,

tests/test_sigv4_helper.py

@@ -307,7 +307,7 @@ def test_create_sigv4_client_default(self, mock_client_class, mock_create_auth):
         result = create_sigv4_client()
 
         # Verify client was created correctly
-        mock_create_auth.assert_called_once_with('your-service', None, None)
+        mock_create_auth.assert_called_once_with('', None, None)
 
         # Check that AsyncClient was called with correct parameters
         call_args = mock_client_class.call_args