Add first set of integration tests

[d-e-s-o]

This change introduces the first set of integration-style test for the
application. Those tests may or may not connect to an actual Nitrokey
device (depending on what they test). We use the nitrokey-test crate's
test attribute macro to automatically dispatch tests to connected
devices or skip them if a required device is not present. It also
provides the means for automatically serializing tests.

[d-e-s-o]

@robinkrahl , would be nice if you could take a look and let me know what you think. Do you think the test organization makes sense? I definitely think that we should not put everything into a single file (as we did for commands.rs). I envisioned splitting by command (only done for status right now), with run.rs containing some more or less generic tests pertaining the execution.

[d-e-s-o]

If you feel that the patch is too big I can split it. I felt that a reasonable amount is boilerplate that does not need a close review.

[robinkrahl]

I’ll have a look at it! Regarding code organization, I think we could also consider splitting commands.rs into submodules (per subcommand).

[d-e-s-o]

Thanks!

Regarding code organization, I think we could also consider splitting commands.rs into submodules (per subcommand).

Yeah, I am looking into preparing a patch that removes some of the command enum related boilerplate (basically auto generating it). Let's see how bad it is after that. I believe there was a reason for the organization, but I don't recall exactly. I may just remember wrongly.

[d-e-s-o]

Thank you :)