* Refactor and comment `rent` module.

* impl_version bump

* Add doc for Exempt

* Simplify code.

* Update bin/node/runtime/src/lib.rs

Co-Authored-By: thiolliere <[email protected]>

* Update frame/contracts/src/exec.rs

Co-Authored-By: Hero Bird <[email protected]>

Co-authored-by: thiolliere <[email protected]>
Co-authored-by: Hero Bird <[email protected]>