Harden UE Wingman request handling and numeric property conversion.

Switch the Wingman protocol to null-delimited JSON, rework the server's
socket buffering and send logic, and document the bugs found during the
review. Also refactor WingProperty's numeric setters into clearer helper
paths while preserving the existing conversion rules.

Plugins/UEWingman/ue-wingman-mcp.py

@@ -68,7 +68,7 @@ def disconnect():
 
 def send_and_receive(message):
     """Send a JSON message to the editor and return the null-terminated response."""
-    data = json.dumps(message) + "\n"
+    data = json.dumps(message) + "\0"
     sock.sendall(data.encode())
 
     result = b""