Now that the ISR callback mechanism (from #14382) costs essentially
zero — just a function pointer registration, no task or queue — enable
wake-on-RX by default for all ESP32 UART instances.
This reduces RX buffer overflow risk by waking the main loop
immediately when data arrives instead of waiting for the ~16ms
select timeout.
Remove the opt-in request_wake_loop_on_rx() API since all ESP32
UART instances now get this automatically.