rust: test on stable

[chrysn]

Contribution description

This

• updates Rust dependencies (pulling in a few changes that enable building on all platforms on beta) already done in {examples,tests}/rust: Rust updates #17806
• changes 21 out of 3 tests/examples to actually run on beta (while the gcoap test stays on nightly, conveniently ensuring that we still have coverage on both, even though it is rather unlikely that things that work on beta (well, at least on stable) break on nightly)
• updates documentation to reflect all that.

Testing procedure

• Green CI

(If it complains about beta not being installed, workers may need a boot)

Issues/PRs references

One more piece of progress for #17526 (now we're testing it as well).

Edit / update

In the interest of not making lives of new users more complicated than necessary, both examples are now still on nightly even though hello world would work on stable -- but in my experience a hello world example is commonly used as a stepping stone / scaffolding, and right now people would need to switch to nightly as soon as they add, eg. SAUL, or enable the shell. (As things are now, GATs are probably stabilized in 1.62, ie. in time for 2022.07, and everything that's wrapped is stable, including CoAP wrappers).

[chrysn]

Of the many build failures stemming from riotbuild and riotci-worker not being updated yet, comsys found one that is actually bad:

   Compiling riot-sys v0.7.4
error[E0554]: `#![feature]` may not be used on the beta release channel
  --> /data/riotbuild/.cargo/registry/src/github.com-1ecc6299db9ec823/riot-sys-0.7.4/src/lib.rs:78:46
   |
78 | #![cfg_attr(target_arch = "riscv32", feature(core_intrinsics))]
   |                                              ^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0554`.
error: could not compile `riot-sys` due to previous error

Will investigate (I know that issue but it should have been worked around already) ...

[chrysn]

Rebased onto #17806 which fixes the RISC-V issue.

[chrysn]

This has now been updated as planned to go to "stable" right away, which is being released. CI can be enabled once the corresponding CI PR has migrated to the workers.

[maribu]

I just saw that the CI run only took 2 minutes, briefly panicked, that realized that this is one of the cases where can_fast_ci_run.py was able to limit the build to one application only :) So everything is fine.

Congratz for the mayor step towards rust on RIOT :) 🎉

[chrysn]

Thanks! Yeah, the 2 minutes are real -- it'll get worse again once Rust based modules are in. At least until changes to modules only run the build tests where these modules are in, then ideally a change to "everything Rust" would cause murdock to run all Rust examples, plus all builds that enable such a module (which would be all SAUL-using examples on microbit-v2, currently).