Remove redundant types/conflicts when integrating voting, committee and aggregation

[tbagrel1]

Currently PerasVoteId is defined as a concrete type taking a PerasVoterId as a field, which is a newtype around a SPO public key. But committee selection API doesn't enforce a concrete voterID, and in current implementations, we use SeatIndex.

Similarly, current Peras architecture uses PerasStakeDistr directly, and PerasVoteStake, while committee abstracts away stake distr, and just expose PerasVoteWeight.

These conflicts need to be resolved as part of the plumbing effort