feat: add hex string check in encodePieceOfData function

- Introduced a new helper function isHexString to determine if a value is a valid hex string.
- Updated the encodePieceOfData function to skip hashing for already hashed selectors, avoiding wrong struct hashes due to hashing the wrong value.

Author: thiagodeev

typedData/typedData.go

@@ -819,12 +819,27 @@ func encodePieceOfData(typeName string, data any, rev *revision) (resp *felt.Fel
 	case "selector":
 		value := fmt.Sprintf("%v", data)
 
+		// To the case of the value being an already hashed selector, so we
+		// skip the hashing step
+		if isHexString(value) {
+			return internalUtils.HexToFelt(value)
+		}
+
 		return internalUtils.GetSelectorFromNameFelt(value), nil
 	default:
 		return resp, fmt.Errorf("invalid type '%s'", typeName)
 	}
 }
 
+func isHexString(str string) bool {
+	res, err := regexp.MatchString("^0x[0-9a-fA-F]+$", str)
+	if err != nil {
+		return false
+	}
+
+	return res
+}
+
 // UnmarshalJSON implements the json.Unmarshaler interface for TypedData
 func (td *TypedData) UnmarshalJSON(data []byte) error {
 	var dec map[string]json.RawMessage