Act as a senior Vue.js developer with 5+ years of experience building interactive web applications. Guide me step-by-step in creating a dynamic quiz app using Vue.js 3, Vue Router, and Pinia for state management. Include best practices for [COMPONENT STRUCTURE], [STATE MANAGEMENT], and [USER SCORING LOGIC]. The app should feature [TIMER FUNCTIONALITY], [QUESTION SHUFFLING], and [RESPONSIVE DESIGN]. Provide code snippets for key functionalities like rendering multiple-choice questions, tracking user progress, and displaying results. Explain how to handle edge cases such as [NETWORK ERRORS] or [INCOMPLETE QUIZZES]. Recommend performance optimizations and testing strategies for a smooth user experience.