refactor: move utility functions to dedicated util package and adjust references

proto_generator/native_decoder.go

@@ -249,7 +249,7 @@ func SwitchDecoder(g *Generator, varToSet ast.Expr, dataRaw any, name string) (s
 	if err != nil {
 		return
 	}
-	for _, fName := range OrderedKeys(data.Fields) {
+	for _, fName := range util.OrderedKeys(data.Fields) {
 		fType := data.Fields[fName]
 		e := MultiTypeFix(fName, &cet)
 		if e == nil {
@@ -324,7 +324,7 @@ func MapperDecoder(g *Generator, varToSet ast.Expr, dataRaw any, name string) (s
 	mName := name + "Map"
 
 	expressions := Exprs()
-	for _, k := range OrderedKeys(data.Mappings) {
+	for _, k := range util.OrderedKeys(data.Mappings) {
 		v := data.Mappings[k]
 		expressions = append(expressions, KeyValueExpr(NumLitStr(k), StrLit(v)))
 	}