feat: add tests for admin checks and error handling

- Introduced new tests for the `is_admin_async` function to verify correct behavior based on user roles.
- Added tests for error handling in the `error_handler` to ensure exceptions are logged and do not propagate.
- Enhanced test coverage for configuration settings by adding a test for parsing admin phone numbers from environment variables.
- Updated the `.cursorrules` file to include the use of a virtual environment for better dependency management.

tests/test_handlers_errors.py

@@ -52,3 +52,26 @@ async def test_error_handler_update_none_does_not_crash():
     context = MagicMock()
     context.error = Exception("test")
     await error_handler(None, context)
+
+
+@pytest.mark.asyncio
+async def test_error_handler_reply_text_raises_does_not_propagate():
+    """error_handler: when reply_text raises, exception is caught and logged; does not propagate."""
+    class FakeUpdate:
+        pass
+
+    update = FakeUpdate()
+    update.effective_message = MagicMock()
+    update.effective_message.reply_text = AsyncMock(
+        side_effect=Exception("reply failed")
+    )
+    update.effective_user = MagicMock()
+    context = MagicMock()
+    context.error = Exception("test error")
+
+    with patch("duty_teller.handlers.errors.Update", FakeUpdate):
+        with patch("duty_teller.handlers.errors.get_lang", return_value="en"):
+            with patch("duty_teller.handlers.errors.t", return_value="An error occurred."):
+                await error_handler(update, context)
+    # Handler must not raise; reply_text was attempted
+    update.effective_message.reply_text.assert_called_once()