core, trie: intermediate mempool between trie and database (#15857)

This commit reduces database I/O by not writing every state trie to disk.

cmd/evm/runner.go

@@ -96,7 +96,9 @@ func runCmd(ctx *cli.Context) error {
 	}
 	if ctx.GlobalString(GenesisFlag.Name) != "" {
 		gen := readGenesis(ctx.GlobalString(GenesisFlag.Name))
-		_, statedb = gen.ToBlock()
+		db, _ := ethdb.NewMemDatabase()
+		genesis := gen.ToBlock(db)
+		statedb, _ = state.New(genesis.Root(), state.NewDatabase(db))
 		chainConfig = gen.Config
 	} else {
 		db, _ := ethdb.NewMemDatabase()