19178: nanocoap_sock: store message ID in nanocoap_sock_t r=benpicco a=benpicco
19186: cpu/gd32v: add periph_rtc support r=benpicco a=gschorcht
### Contribution description
This PR provides the `periph_rtc` support and is one of a bunch of follow up PRs that complete the peripheral drivers for GD32VF103.
### Testing procedure
`tests/periph_rtc` should work and should give the following output:
```
Help: Press s to start test, r to print it is ready
START
main(): This is RIOT! (Version: 2023.04-devel-144-gc17695-cpu/gd32v/periph_rtc)
RIOT RTC low-level driver test
This test will display 'Alarm!' every 2 seconds for 4 times
Setting clock to 2020-02-28 23:59:57
Clock value is now 2020-02-28 23:59:57
Setting alarm to 2020-02-28 23:59:59
Alarm is set to 2020-02-28 23:59:59
Alarm cleared at 2020-02-28 23:59:57
No alarm at 2020-02-28 23:59:59
Setting alarm to 2020-02-29 00:00:01
Alarm!
Alarm!
Alarm!
Alarm!
```
### Issues/PRs references
Co-authored-by: Benjamin Valentin <benjamin.valentin@bht-berlin.de>
Co-authored-by: Gunar Schorcht <gunar@schorcht.net>
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