Store and compute node/stake state in EpochStakes struct

[carllin]

Problem

1. EpochStakes cloned Stakes on every new bank, potentially expensive
2. No convenient way to find epoch-based information critical to consensus like mappings from node ids to vote accounts, vote accounts to authorized voters, total epoch stake.

Summary of Changes

1. Wrap EpochStakes in Arc's to prevent expensive clones on each Bank, only needs to be recomputed when crossing leader_schedule_epoch boundaries
2. Save off Epoch-based information and add convenience functions

Note @mvines this breaks the ABI (serializing/deserializing the bank), I've add this to track here: https://github.com/solana-labs/solana/projects/45

Fixes #

[mvines]

😢 we'll need to halt and restart devnet, tds, and mainnet-beta with a snapshot rewrite. I'll look more closely at this PR tomorrow @carllin

[carllin]

😢 we'll need to halt and restart devnet, tds, and mainnet-beta with a snapshot rewrite. I'll look more closely at this PR tomorrow @carllin

Ugh, I know hehe. I debated stashing this info elsewhere but it started getting really ugly/hacky, so I bit the bullet.

[carllin]

@aeyakovenko, fyi, the mapping from the node_id used in gossip to the set of vote_account's is fixed here at leader_schedule_epoch boundaries (Aka the mappinig for epoch n+2 is fixed halfway through epoch n). Hopefully that should be ok

[mvines]

I'd like to find a way to roll this out without having to hard fork mainnet-beta

[sakridge]

I'd like to find a way to roll this out without having to hard fork mainnet-beta

+1, these kinds of things are just kind of a cache/wrapper over some account state, we need to figure out how to handle that sooner than later I think.

[aeyakovenko]

@mvines @carllin if the state is derived from the account state, do we need to store it in the snapshot? Can it be recomputed at load?

[carllin]

@aeyakovenko, because the EpochStakes for the current epoch are saved off from the stakes 1.5 epochs ago, it's not entirely derivable, you need the stake information from that point in time.

Pull request has been modified.

[carllin]

@mvines bumped it here

[codecov]

Codecov Report

Merging #8958 into master will decrease coverage by <.1%.
The diff coverage is 73.4%.

@@           Coverage Diff            @@
##           master   #8958     +/-   ##
========================================
- Coverage    80.4%   80.3%   -0.1%     
========================================
  Files         267     268      +1     
  Lines       58543   58684    +141     
========================================
+ Hits        47073   47174    +101     
- Misses      11470   11510     +40