Optimize stakes cache and rewards at epoch boundaries (#20432)

* Optimize stakes cache and rewards at epoch boundaries

* Fetch from accounts db

* Add cli flag for disabling epoch boundary optimization

local-cluster/src/validator_configs.rs

@@ -60,6 +60,7 @@ pub fn safe_clone_config(config: &ValidatorConfig) -> ValidatorConfig {
         no_wait_for_vote_to_start_leader: config.no_wait_for_vote_to_start_leader,
         accounts_shrink_ratio: config.accounts_shrink_ratio,
         accounts_db_config: config.accounts_db_config.clone(),
+        disable_epoch_boundary_optimization: config.disable_epoch_boundary_optimization,
     }
 }