Enable mypy strict compliance

oin_thermostat/__main__.py

@@ -8,7 +8,7 @@ logger = logging.getLogger(__name__)
 config_path = "config.toml"
 
 
-def main():
+def main() -> int:
     with open(config_path, "rb") as config_file:
         config = tomllib.load(config_file)
 
@@ -18,7 +18,7 @@ def main():
     if ha_config is None:
         logger.error(f"Missing home assistant config in <{config_path}>")
         logger.error(f"\t{config}")
-        sys.exit(1)
+        return 1
 
     client = HAClient(
         ha_config.get("entity"),
@@ -26,10 +26,16 @@ def main():
         mqtt_config=ha_config.get("mqtt"),
     )
 
-    client.connect()
+    code = client.connect()
+    if code != 0:
+        return 1
 
-    client.loop()
+    code = client.loop()
+    if code != 0:
+        return 1
+
+    return 0
 
 
 if __name__ == "__main__":
-    main()
+    sys.exit(main())