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.

vehicle.go

@@ -792,6 +792,7 @@ func (v *Vehicle) GetFeaturesList() {
 }
 
 // executeServiceRequest
+// Executes a service request to the Subaru API and handles the response.
 func (v *Vehicle) executeServiceRequest(params map[string]string, reqUrl, pollingUrl string, ch chan string, attempt int) error {
 	var maxAttempts = 15