Add on-target-tests and prepare for async implementation

[ithinuel]

Using 2.2kOhm pull-ups on SDA & STL, this impl can reach the target 400KHz in release mode.

Write operation on a 10bit address:

Read operation on a 10bit address:

The tests run the bus at 200kHz to avoid requiring external pull-ups.

[jannic]

While I didn't have time for a full review yet, my first impression is very good. Having tests running on real hardware is a great improvement for such a crate!

[jannic]

Very nicely readable code, great work!
I can't claim that I followed every step in the implemented I²C state machine, but scanning through it, it all looked very convincing. Together with the working on-target test, I have no doubts that this is fine.
Very useful approach to verify the I²C communication against the hardware peripheral on the same chip!

[ithinuel]

Thank you !
I started looking at adding the async pio support but it is much less straightforward.

I am busy with something right now and for a little while so the next update will probably take a couple of months :(

[jannic]

I think we should do a release based on rp2040-hal 0.10.0, as it is needed for updating the BSPs.
And even without async support, I think the tests are a good addition.
What do you think about merging this pr and creating a release, and deferring async support for now?

[ithinuel]

I think that’s a great idea :)