Feature Gate: updates rewards at epoch boundary using cached accounts

[behzadnouri]

Description

When rewards are calculated at the epoch boundary, stake and vote account are loaded from accounts-db, which is slow.
#24200 will instead use cache stake and vote accounts in Bank.stakes.

These cached accounts are synchronized with accounts-db after each transaction, and so there should not be any change in the resulting computation:
https://github.com/solana-labs/solana/blob/d2702201c/runtime/src/bank.rs#L4526
Nevertheless, to avoid any chances of introducing a consensus issue, the switch to cached account is feature gated.

Feature ID

28s7i3htzhahXQKqmS2ExzbEoUypg9krwvtK2M9UWXh9

Activation Method

Single Core Contributor

Testnet Activation Epoch

470

Devnet Activation Epoch

506

Mainnet-Beta Activation Epoch

477