chore(mempool): move a check in commit_block into a util (#2016)

This is a prep. refactor for small diffs. in nonce abstraction feature.

crates/starknet_mempool/src/mempool.rs

@@ -138,19 +138,7 @@ impl Mempool {
 
         // Align mempool data to committed nonces.
         for (&address, &next_nonce) in &address_to_nonce {
-            // FIXME: Remove after first POC.
-            // If commit_block wants to decrease the stored account nonce this can mean one of two
-            // things:
-            // 1. this is a reorg, which should be handled by a dedicated TBD mechanism and not
-            //    inside commit_block
-            // 2. the stored nonce originated from add_tx, so should be treated as tentative due
-            // to possible races with the gateway; these types of nonces should be tagged somehow
-            // so that commit_block can override them. Regardless, in the first POC this cannot
-            // happen because the GW nonces are always 1.
-            if let Some(&stored_nonce) = self.account_nonces.get(&address) {
-                assert!(stored_nonce <= next_nonce, "NOT SUPPORTED YET {address:?} {next_nonce:?}.")
-            }
-
+            self.validate_committed_nonce(address, next_nonce);
             let account_state = AccountState { address, nonce: next_nonce };
             self.align_to_account_state(account_state);
         }
@@ -217,6 +205,21 @@ impl Mempool {
         Ok(())
     }
 
+    fn validate_committed_nonce(&self, address: ContractAddress, next_nonce: Nonce) {
+        // FIXME: Remove after first POC.
+        // If commit_block wants to decrease the stored account nonce this can mean one of two
+        // things:
+        // 1. this is a reorg, which should be handled by a dedicated TBD mechanism and not inside
+        //    commit_block
+        // 2. the stored nonce originated from add_tx, so should be treated as tentative due
+        // to possible races with the gateway; these types of nonces should be tagged somehow
+        // so that commit_block can override them. Regardless, in the first POC this cannot
+        // happen because the GW nonces are always 1.
+        if let Some(&stored_nonce) = self.account_nonces.get(&address) {
+            assert!(stored_nonce <= next_nonce, "NOT SUPPORTED YET {address:?} {next_nonce:?}.")
+        }
+    }
+
     fn enqueue_next_eligible_txs(&mut self, txs: &[TransactionReference]) -> MempoolResult<()> {
         for tx in txs {
             let current_account_state = AccountState { address: tx.address, nonce: tx.nonce };