A list of the last 100 skipped epochs and the corresponding session index
when the epoch was skipped.
This is only used for validating equivocation proofs. An equivocation proof
must contains a key-ownership proof for a given session, therefore we need a
way to tie together sessions and epoch indices, i.e. we need to validate that
a validator was the owner of a given key on a given session, and what the
active epoch index was during that session.
A list of the last 100 skipped epochs and the corresponding session index when the epoch was skipped.
This is only used for validating equivocation proofs. An equivocation proof must contains a key-ownership proof for a given session, therefore we need a way to tie together sessions and epoch indices, i.e. we need to validate that a validator was the owner of a given key on a given session, and what the active epoch index was during that session.