/* The developer was tasked with writing a notification sending service. Requirements: - The Send method should send messages in parallel. - No more than maxworkers HTTP requests can be executed simultaneously. - If at least one send fails, stop the rest and return an error. - The method should handle context cancellation properly. - All resources should be released correctly. - The method can be called concurrently from different goroutines. - The Client should keep track of the number of successfully sent messages. Review the code, find issues, and fix it.