Bump `rand` crate to 0.9

Currently, rand crate is used with version 0.8: https://github.com/arkworks-rs/std/blob/b0cbdeb097b42f61880b3bee19e8dd37258d23a5/Cargo.toml#L16

We should bump this to 0.9 (https://github.com/rust-random/rand/releases/tag/0.9.0)