Fix issue where the GUI main thread was consuming excessive CPU while
waiting for background tasks to complete.
By adding a configurable sleep interval between UI updates,
CPU usage is significantly reduced while maintaining responsiveness.
- Add thread_sleep_interval constant to global Constants class
- Implement wait_for_thread utility function in gui_support
- Update all wxPython event loops to use the new helper
- Test shows approximately 60% CPU usage reduction during waits