Enhance MySubaru API integration with improved error handling and new utility functions

- Refactor Response struct's parse method to return detailed error messages based on API error codes.
- Introduce UnixTime type for handling Unix timestamps in JSON marshaling and unmarshaling.
- Add email masking utility function to obfuscate email addresses for privacy.
- Implement containsValueInStruct function to check for substring presence in struct fields.
- Create comprehensive unit tests for UnixTime, email masking, and struct value checking.
- Update vehicle service request method documentation for clarity.

utils.go

@@ -1,7 +1,10 @@
 package mysubaru
 
 import (
+	"fmt"
 	"math"
+	"net/mail"
+	"reflect"
 	"regexp"
 	"strconv"
 	"strings"
@@ -114,6 +117,65 @@ func transcodeDigits(vin string) int {
 	return digitSum
 }
 
+// emailMasking takes an email address as input and returns a version of the email
+// with the username part partially hidden for privacy. Only the first and last
+// characters of the username are visible, with the middle characters replaced by asterisks.
+// The function validates the email format before processing.
+// Returns the obfuscated email or an error if the input is not a valid email address.
+func emailMasking(email string) (string, error) {
+	_, err := mail.ParseAddress(email)
+	if err != nil {
+		return "", fmt.Errorf("invalid email address: %s", email)
+	}
+
+	re1 := regexp.MustCompile(`^(.*?)@(.*)$`)
+	matches := re1.FindStringSubmatch(email)
+
+	var username, domain string
+	if len(matches) == 3 { // Expecting the full match, username, and domain
+		username = matches[1]
+		domain = matches[2]
+	} else {
+		return "", fmt.Errorf("invalid email format: %s", email)
+	}
+
+	re2 := regexp.MustCompile(`(.)(.*)(.)`)
+
+	replacedString := re2.ReplaceAllStringFunc(username, func(s string) string {
+		firstChar := string(s[0])
+		lastChar := string(s[len(s)-1])
+		middleCharsCount := len(s) - 2
+
+		if middleCharsCount < 0 { // Should not happen with the length check above, but for robustness
+			return s
+		}
+		return firstChar + strings.Repeat("*", middleCharsCount) + lastChar
+	})
+
+	return replacedString + "@" + domain, nil
+}
+
+// containsValueInStruct checks if any string field in the given struct 's' contains the specified 'search' substring (case-insensitive).
+// It returns true if at least one string field contains the substring, and false otherwise.
+// If 's' is not a struct, it returns false.
+func containsValueInStruct(s any, search string) bool {
+	val := reflect.ValueOf(s)
+	if val.Kind() != reflect.Struct {
+		return false // Not a struct
+	}
+
+	for i := 0; i < val.NumField(); i++ {
+		field := val.Field(i)
+		if field.Kind() == reflect.String {
+			if strings.Contains(strings.ToLower(field.String()), strings.ToLower(search)) {
+				return true
+			}
+		}
+	}
+
+	return false
+}
+
 // timeTrack .
 // func timeTrack(name string) {
 // 	start := time.Now()