This updates the test app to use the XFA shell interface and ztimer.
In addition, a shell command to power off the UART interface is added
to e.g. confirm that power consumption indeed goes down.
Also the LF is display inside the [...].
Now it is more obvious what characters came in on the RX port of the UART.
Here is an example:
2024-01-20 20:57:41,368 # send 1 ati
2024-01-20 20:57:41,368 # UART_DEV(1) TX: ati
> 2024-01-20 20:57:41,393 # Success: UART_DEV(1) RX: [ati\r\r\n]
2024-01-20 20:57:41,398 # Success: UART_DEV(1) RX: [SARA-N310-00X-00\r\n]
2024-01-20 20:57:41,399 # Success: UART_DEV(1) RX: [\r\n]
2024-01-20 20:57:41,399 # Success: UART_DEV(1) RX: [OK\r\n]