Upgrade rust edition to 2024 from 2021

[linear]

Currently we have 2024 in rustfmt and rust 2021 in cargo toml. To keep it in sync we want to make sure to use edition 2024. This brings unsafe changes to how set var, set env etc. https://doc.rust-lang.org/edition-guide/rust-2024/newly-unsafe-functions.html

Make changes to specify unsafe for set vars.