added in micropython external library for const feature.

it's returing valid attribute arrays, that just need converted on z2m
side.

it's also respecting the stop command from the console, which I will
attempt to expose as just a button press.

venv/Lib/site-packages/serial/urlhandler/protocol_rfc2217.py

@@ -0,0 +1,12 @@
+#! python
+#
+# This is a thin wrapper to load the rfc2217 implementation.
+#
+# This file is part of pySerial. https://github.com/pyserial/pyserial
+# (C) 2011 Chris Liechti <cliechti@gmx.net>
+#
+# SPDX-License-Identifier:    BSD-3-Clause
+
+from __future__ import absolute_import
+
+from serial.rfc2217 import Serial  # noqa