cpu/native: Enable Rust on 64bit

[chrysn]

Contribution description

This updates the riot-sys dependency and then removes the lock-out of Rust on NATIVE_64BIT builds.

Testing procedure

• Green CI

Issues/PRs references

Back in #20315, Rust was excluded because it had build failures. RIOT-OS/rust-riot-sys#40 works around the failures.

Thanks @fzi-haxel for preparing everything!

[edit:] Found some more errors, which so far all look like i32 vs isize mismatches. I'm on it; definitely easier to fix here than when some 16bit arch support is added :-D

[riot-ci]

Murdock results

✔️ PASSED

7587c77 boards/native64/doc: Remove Rust note

Success	Failures	Total	Runtime
10009	0	10009	10m:22s

Artifacts

• Documentation preview

[chrysn]

Builds now, please review.

Total toll of trouble:

• At one point, I used i32 in the wrappers when the API really says ssize_t (and u32 / size_t in the same file)
• c2rust tries generating full varargs for vprintf on the native architecture more successfully than on the odd ones -- but varargs are not stable. A workaround ensures that that vprintf passes but is unusable, as we're not using it anyway (that it's there in the first place is an effect of not being able to import "just the static functions in that header", because the header includes other files, so we get all the functions anywhere).

[fzi-haxel]

I am not a Rust expert, but looks good to me and the examples/tests run.
#20335 changes cpu/native/Makefile.features a bit, but would be an easy rebase.

[fzi-haxel]

Since #20335 was merged first, could you remove the reference to the missing Rust support in boards/native64/doc.txt when rebasing to master?

[benpicco]

This needs a rebase

[chrysn]

Thanks for reviews and nudge. Rebased, and tested with the rust-gcoap example and ./aiocoap-client 'coap://[fe80::3c63:beff:fe85:ca96%tapbr0]:5683/vfs/large'.