WIP: Bump to rand[_core] 0.9

[pinkforest]

Pending / Clarifications

• Breaking/Minor (Opt-in): Requires MSRV 1.63 - need to bump from current 1.60
• Breaking/Minor (Opt-in): rand_core 0.9 via API
• Breaking/Minor (Opt-in): We need to implement TryCryptoRng which needs API changes from current infallible API.
• group and ff needs to bump rand + rand_core - Bump rand + rand_core zkcrypto/group#55

Notes

• warning: use of deprecated function rand::thread_rng: renamed to rng <-- was renamed
• CryptoRngCore no more: Rework CryptoRng rust-random/rand#1273
• 0.9 OsRng does not seem to implement CryptoRng ? rust-random/rand#1561
• ThreadRng and OsRng implement diff Try/CryptoRng traits rust-random/rand#1566
• rand_core/getrandom is no more pub - Make getrandom a non-pub dep; rename feature to os_rng rust-random/rand#1537
• Let rand::rng() use OsRng unless thread_rng is enabled? rust-random/rand#1545

[tarcieri]

@pinkforest it needs to be os_rng now

[NimonSour]

Since rand_core changed the trait for OsRng from CryptoRngCore( which is RngCore + CryptoRng ) to TryRngCore +TryCryptoRngit makes sense to keep all the methods of types across dalek crates that are dependent on CryptoRngCore ( like generate and random ) as R : RngCore + CryptoRng plus adding the additional methods ( try_generate and try_random ) respectively where R : TryRngCore + CryptoRngCore.

Example for ed25519/src/signing.rs

    pub fn generate<R: RngCore + CryptoRng + ?Sized>(csprng: &mut R) -> SigningKey {
        let mut secret = SecretKey::default();
        csprng.fill_bytes(&mut secret);
        Self::from_bytes(&secret)
    }
    
    pub fn try_generate<R: TryRngCore + TryCryptoRng + ?Sized>(csprng: &mut R) -> Result<SigningKey,<R as TryRngCore>::Error> {
        let mut secret = SecretKey::default();
        csprng.try_fill_bytes(&mut secret)?;
        Ok(Self::from_bytes(&secret))
    }

It will offer some backward compatibility while aligning with rand_core's RngCoreand TryRngCore traits, where the user has a choice on RNG implementation.

[tarcieri]

it makes sense to keep all the methods of types across dalek crates that are dependent on CryptoRngCore ( like generate and random ) as R : RngCore + CryptoRng

CryptoRng now has a supertrait bound on RngCore, so instead CryptoRngCore should just be replaced with just CryptoRng. Adding RngCore + ... is redundant due to the supertrait bound. See:

https://docs.rs/rand_core/0.9.0/rand_core/trait.CryptoRng.html

Also you can call OsRng.unwrap_err() to get a CryptoRng-friendly version of OsRng.

[pinkforest]

I assume we can live with ff/group will get duplicate 0.8 rand until ff/group upgrades - unblocking us to adopt 0.9 ?