bump defmt to v1, bump rand dev-dep to v0.9

[robamu]

No description provided.

[AudaciousAxiom]

I'm not a maintainer of this project, but this PR might be more straightforward to review if it were only about the bump of defmt to v1, as the bump of rand might require more consideration (even if it is only a dev-dependency). (Also the latest release of rand is v0.10 now).

Bumping defmt to v1 shouldn't be a breaking change as v0.3.100 implements the SemVer trick: v0.3.100's re-exports the defmt::Format trait from v1, so the trait being used right now is already that of v1.

Additionally, the announcement post of v1 explicitly says that it is safe to do so:

Any library currently using defmt = "^0.3" in their Cargo.toml file can replace that line with defmt = "1", and everything will continue to work, unless you are locked to a version of 0.3 prior to the final 1.0-compatible version.

[eldruin]

Done in #172 . Thank you for your work!