This module expose one function
P_NPoS (Payout NPoS) or
compute_total_payout which returns
the total payout for the era given the era duration and the staking rate in NPoS.
The staking rate in NPoS is the total amount of tokens staked by nominators and validators,
divided by the total token supply.
- The total payout to all validators (and their nominators) per era and maximum payout.