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

[Victor239]

This resolves #206 and #344. I had been having these CPU usage issues for a long time, this fix completely solved my issues.

The server event loop was consuming up to 100% CPU due to a single-line bug where rlist and xlist referenced the same list object, causing select.select() to monitor identical sockets for both read and exceptional events.

Changes:

• Fixed line 264 in etesync_dav/radicale_main/server.py:

  # Before: both variables reference the same list
  rlist = xlist = []
  
  # After: separate list objects
  rlist, xlist = [], []
  

This ensures xlist remains empty as intended, allowing the event loop to properly block until events occur instead of busy-looping.