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)

Start at the rand dependency entry in Cargo.toml, linked at line 16, and read the rand 0.9.0 release notes for upgrade changes. Update the dependency to 0.9 and verify that the project still builds and its checks pass; done means the repository uses rand 0.9 successfully.

Written by the indexing model from the issue text.