add a couple interfaces to libevm

Author: Darioush Jalali

libevm/libevm.go

@@ -40,6 +40,14 @@ type StateReader interface {
 	SlotInAccessList(addr common.Address, slot common.Hash) (addressOk bool, slotOk bool)
 }
 
+type StateDB interface {
+	StateReader
+}
+
+type PredicateResults interface {
+	GetPredicateResults(txHash common.Hash, address common.Address) []byte
+}
+
 // AddressContext carries addresses available to contexts such as calls and
 // contract creation.
 //