test(debug): add unit tests for condition evaluation, line lookup and

RFLAGS decoding

Assisted-by: MiniMax M3

debug/repl.go

@@ -538,7 +538,7 @@ func decodeRflags(f uint64) string {
 		flags += "OF "
 	}
 	if flags == "" {
-		flags = "none"
+		return "none"
 	}
 	return flags[:len(flags)-1] // trim trailing space
 }