fix: apply ruff formatting to http_client.py

Fixed formatting in file handle cleanup code to match project style.
Changed single quotes to double quotes as per ruff requirements.

Author: jdrhyne

src/nutrient_dws/http_client.py

@@ -170,11 +170,11 @@ def post(
         # Clean up file handles after request
         if files:
             for _, file_data in files.items():
-                if hasattr(file_data, 'close'):
+                if hasattr(file_data, "close"):
                     file_data.close()
                 elif isinstance(file_data, tuple) and len(file_data) > 1:
                     file_obj = file_data[1]
-                    if hasattr(file_obj, 'close'):
+                    if hasattr(file_obj, "close"):
                         file_obj.close()
 
         return self._handle_response(response)