fix and improve shootout-chameneos-redux

* fix official shootout test (spacing)
* use libgreen to improve performances
* simplify and modernize code
* remove warnings
auto merge of #13667 : TeXitoi/rust/shootout-chameneos-redux-fix, r=alexcrichton

* fix official shootout test (spacing)
* use libgreen to improve performances
* simplify and modernize code
* remove warnings