core/vm: make all opcodes proper type (#30925)

Noticed this omission while doing some work on goevmlab. We don't
properly type some of the opcodes, but apparently implicit casting works
in all the internal usecases.

core/vm/opcodes.go

@@ -164,7 +164,7 @@ const (
 
 // 0x80 range - dups.
 const (
-	DUP1 = 0x80 + iota
+	DUP1 OpCode = 0x80 + iota
 	DUP2
 	DUP3
 	DUP4
@@ -184,7 +184,7 @@ const (
 
 // 0x90 range - swaps.
 const (
-	SWAP1 = 0x90 + iota
+	SWAP1 OpCode = 0x90 + iota
 	SWAP2
 	SWAP3
 	SWAP4