Bump rand core to 0.9.1 and rand to 0.9.0

[aurelj]

This is kind of a follow-up on #3360.

Note that rand_core now provides a default implementation for TryRngCore so try_fill_bytes() is automatically implemented.

[aurelj]

Note that the failed test is due to ed25519_dalek depending on an old version of rand_core.
See dalek-cryptography/curve25519-dalek#729

[Dirbaio]

lgtm, but then we need to wait for an ed25519_dalek release

alternatively we could impl both the 0.6 and 0.9 trait, similar to how we do with embedded-hal 0.2 and 1.0

[aurelj]

The rand_core feature of ed25519-dalek is actually only enabled in the dev-dependencies of embassy-boot and only for one test. I just reverted back the rand crate dev-dependencies of embassy-boot to 0.8 for this single test and everything works fine now.