chore: add test of random powers FinalityProviderDistInfo until expire

[RafilxTenfen]

In general it is nice that events now incrementaly adjust voting power as this makes it possible to create nice propery based test in which:

we create random amount of delegations with random power
unbond some of them by on demand unbonding
let others expire
At the end of the test voting power of the FinalityProviderDistInfo should be 0

ref: #306 (comment)