Real Time Clock support and examples

[Remus7]

Pull Request Overview

This pull request adds Real Time Clock support for libtock-c apps. Specifically, in libtock folder were added rtc.c and rtc,h, which communicate with the date_time capsule from another pull requst to the main tock repository (tock/tock#3559). Additionally, in the examples folder was added an example rtc app, which firs sets a time and date at the beggining and then prints updated time every second.

Testing Strategy

This pull request was tested by running the example project provided on the nucleo-stm429zi and raspberry pi pico boards.

[ppannuto]

It's not a huge deal, but probably better to not have an idiom of large(?) struct-copying floating around libtock (said, without checking if we are doing that elsewhere that we shouldn't be..).

Otherwise this looks good, and is just blocked on the kernel interface settling / being merged.

[Remus7]

Thank you for the suggestions, I have merged the changes into the project. However, this week I will be unable to test whether this program still runs as expected, since I do not have access to a board with date_time support. I will try to test this again around next week, but otherwise, the requested changes have been updated.

[Remus7]

I checked the example project now, and it works as intended, including the changes that were made to the main tock capsule

[ppannuto]

Great, this is ready to go once the kernel side is merged. We generally defer libtock merges until the kernel merge lands.

[Remus7]

The changes to the main tock repository have been merged.