core: turn gas into a vector <regularGas, stateGas>

core/vm/gascosts.go

@@ -0,0 +1,17 @@
+package vm
+
+import "fmt"
+
+type GasCosts struct {
+	RegularGas uint64
+	StateGas   uint64
+}
+
+// Sum returns the total gas (regular + state).
+func (g GasCosts) Sum() uint64 {
+	return g.RegularGas + g.StateGas
+}
+
+func (g GasCosts) String() string {
+	return fmt.Sprintf("<%v,%v>", g.RegularGas, g.StateGas)
+}