PRE-M8-T02: add read-only WarmteLink serial probe

requirements.in

@@ -7,6 +7,7 @@ paho-mqtt>=2.0,<3.0
 pymodbus>=3.6,<4.0
 pydantic-settings>=2.6,<3.0
 pyotp>=2.9,<3.0
+pyserial>=3.5,<4.0
 python-multipart>=0.0.12,<1.0
 pyyaml>=6.0,<7.0
 sqlalchemy>=2.0,<3.0