Since we're implementing rules for `StakeManager` migrations, we need
multiple instances inside the certora specs.
This results in the prover trying to run rules on the other
`StakeManager` instance as well, which isn't always desired,
as it causes some rules to fail, even though they'd pass if they'd be
executed only on the `currentContract`.
This commit makes the filter condition for relevant rules stronger, such
that the prover will not run them on the `newStakeManager` contract
instance.
There have been a bunch of breaking changes in the staking contract that
resulted in our specs not compiling.
This commit fixes this, however it does not yet ensure the prover is
satisfied.