Fix high CPU usage from shared list reference in select() event loop (#361)

* Initial plan

* Fix high CPU usage bug in server event loop

Changed line 264 in etesync_dav/radicale_main/server.py from:
  rlist = xlist = []
to:
  rlist, xlist = [], []

This fixes a critical bug where both variables pointed to the same list,
causing select.select() to receive the same sockets for both readable
and exceptional conditions, leading to inefficient event handling and
high CPU usage.

Co-authored-by: Victor239 <12621257+Victor239@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Victor239

etesync_dav/radicale_main/server.py

@@ -261,7 +261,7 @@ def serve(configuration, shutdown_socket):
         max_connections = configuration.get("server", "max_connections")
         logger.info("Radicale server ready")
         while True:
-            rlist = xlist = []
+            rlist, xlist = [], []
             # Wait for finished clients
             for server in servers.values():
                 rlist.extend(server.client_sockets)