The index of the last block in the finalized part of the chain is kept
Finalization can be requested at any point, by anyone, and entails just checking if the finality period of first children of last finalized is finished.
In removal, the blocks that are recursively deleted are refunded to those who proposed them
TODO / NEW ISSUE : When finalizing, remove all siblings (block that will no longer be candidates for finalization
TODO / NEW ISSUE : When finalizing, remove all siblings (block that will no longer be candidates for finalization