[x] Deprecate the async Windows tx_rx_task so a backport to 0.5 will give warnings
[x] Park the TX/RX threads when there's nothing in flight to save CPU
[x] Have a look at async-spin-sleep and see what performance and CPU usage is like, with a mind to recommending it for applications that still require async timers.
TODO
tx_rx_taskso a backport to 0.5 will give warningsasync-spin-sleepand see what performance and CPU usage is like, with a mind to recommending it for applications that still requireasynctimers.