Refactor epoch reward 1 (solana-labs#27253)

* refactor: extract store_stake_accounts fn

* clippy: slice

Co-authored-by: haoran <haoran@mbook>

runtime/src/bank.rs

@@ -3280,6 +3280,17 @@ impl Bank {
             .for_each(|x| rewards.push((x.stake_pubkey, x.stake_reward_info)));
     }
 
+    fn store_stake_accounts(&self, stake_rewards: &[StakeReward], metrics: &mut RewardsMetrics) {
+        // store stake account even if stakers_reward is 0
+        // because credits observed has changed
+        let mut m = Measure::start("store_stake_account");
+        self.store_accounts((self.slot(), stake_rewards));
+        m.stop();
+        metrics
+            .store_stake_accounts_us
+            .fetch_add(m.as_us(), Relaxed);
+    }
+
     fn update_recent_blockhashes_locked(&self, locked_blockhash_queue: &BlockhashQueue) {
         #[allow(deprecated)]
         self.update_sysvar_account(&sysvar::recent_blockhashes::id(), |account| {