Contribution description

The first change is to improve the visibility of incoming CRs (carriage return). They will now be shown as \r. Also, the LF (that usually comes after a CR) is now shown inside [..], not after the closing ].

The second change is a re-implementation of PR20128. I hope that @benpicco is not offended by it. I had this change lying around for more than a year, sorry about that. I want to include the change in the current PR because I consider the code in PR20128 too "hackish".

Testing procedure

I've tested the change on a sodaq-sara-sff board which has a Ublox SARA N310. For that a few extra steps are needed because the Ublox needs two pins to be ON, plus one pin needs to be toggled low for roughly one second. Otherwise the Ublox remains off.
After that:

• init 1 38400
• eol_cr
• send 1 AT

Here is an example what you can expect.

> init 1 38400
2024-01-21 17:16:51,910 # init 1 38400
2024-01-21 17:16:51,910 # Success: Initialized UART_DEV(1) at BAUD 38400
2024-01-21 17:16:52,161 # UARD_DEV(1): test uart_poweron() and uart_poweroff()  ->  [OK]
> eol_cr
2024-01-21 17:16:56,461 # eol_cr
> send 1 AT
2024-01-21 17:17:02,141 # send 1 AT
2024-01-21 17:17:02,142 # UART_DEV(1) TX: AT
> 2024-01-21 17:17:02,167 # Success: UART_DEV(1) RX: [AT\r\r\n]
2024-01-21 17:17:02,168 # Success: UART_DEV(1) RX: [OK\r\n]

Issues/PRs references

None