core: transaction pool optimizations (#21328)

* core: added local tx pool test case

* core, crypto: various allocation savings regarding tx handling

* core/txlist, txpool: save a reheap operation, avoid some bigint allocs

Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>

core/tx_pool.go

@@ -1059,8 +1059,8 @@ func (pool *TxPool) runReorg(done chan struct{}, reset *txpoolResetRequest, dirt
 
 	// Update all accounts to the latest known pending nonce
 	for addr, list := range pool.pending {
-		txs := list.Flatten() // Heavy but will be cached and is needed by the miner anyway
-		pool.pendingNonces.set(addr, txs[len(txs)-1].Nonce()+1)
+		highestPending := list.LastElement()
+		pool.pendingNonces.set(addr, highestPending.Nonce()+1)
 	}
 	pool.mu.Unlock()
 
@@ -1457,6 +1457,10 @@ func (as *accountSet) contains(addr common.Address) bool {
 	return exist
 }
 
+func (as *accountSet) empty() bool {
+	return len(as.accounts) == 0
+}
+
 // containsTx checks if the sender of a given tx is within the set. If the sender
 // cannot be derived, this method returns false.
 func (as *accountSet) containsTx(tx *types.Transaction) bool {