Resolve "replace `Succ` with an `Add` constructor on `Level`" ✨️

Closes #95 🐔️👍️
Approved-by: aalbert <augustin.albert@bleu-azure.fr>
Approved-by: loutr <l.ta-ma@proton.me>

🦀️🍰🦀️🍰🦀️🍰

* chore(cargo deny): cargo update + temporary cargo deny modification to allow duplicate dependency versions

* fix(kernel, level): remove useless memoization + some minor simplifications

* fix(kernel): use u32 in order to have safe conversions to i64

* fix(kernel): wrap int conversion

* feat(kernel): replace `Succ` constructor with `Add`