feat: add string to map in httpx parse method (#2459)

* chore: add string to map in httpx parse method

* feat: add httpx parse stringToMap method test

core/mapping/unmarshaler.go

@@ -207,6 +207,8 @@ func (u *Unmarshaler) processFieldNotFromString(field reflect.StructField, value
 		return u.fillMap(field, value, mapValue)
 	case valueKind == reflect.String && typeKind == reflect.Slice:
 		return u.fillSliceFromString(fieldType, value, mapValue)
+	case valueKind == reflect.String && typeKind == reflect.Map:
+		return u.fillMapFromString(value, mapValue)
 	case valueKind == reflect.String && derefedFieldType == durationType:
 		return fillDurationValue(fieldType.Kind(), value, mapValue.(string))
 	default:
@@ -530,6 +532,23 @@ func (u *Unmarshaler) fillSliceFromString(fieldType reflect.Type, value reflect.
 	return nil
 }
 
+func (u *Unmarshaler) fillMapFromString(value reflect.Value, mapValue interface{}) error {
+	switch v := mapValue.(type) {
+	case fmt.Stringer:
+		if err := jsonx.UnmarshalFromString(v.String(), value.Addr().Interface()); err != nil {
+			return err
+		}
+	case string:
+		if err := jsonx.UnmarshalFromString(v, value.Addr().Interface()); err != nil {
+			return err
+		}
+	default:
+		return errUnsupportedType
+	}
+
+	return nil
+}
+
 func (u *Unmarshaler) fillSliceValue(slice reflect.Value, index int,
 	baseKind reflect.Kind, value interface{}) error {
 	ithVal := slice.Index(index)