Court: Fix jurors burned tokens accounting

[facuspagnuolo]

For regular appeal rounds, tokens of the slashed jurors are burned and re-distributed between the winning jurors. OTOH, for final appeal rounds, we burn the tokens of all the jurors participating in it and then re-assign the tokens of the winning jurors along with re-distributing the tokens of the losing jurors between the winning ones.

The problem is that the burn balance is never decreased. Ofc, this is not harmful but accounting does not match correctly.

I propose introducing a new term to handle this since it is not actually a tokens burn (burned tokens are supposed to be burned forever). We should model sth similar to a "lock" and differentiate it from the actual locking we have in the jurors registry currently.