Design a scalable API for a ride-sharing application. Discuss how you would handle authentication, rate limiting, and data storage.

LeetCode #133 - Clone Graph: Given a reference of a node in a connected undirected graph, return a deep copy (clone) of the graph. Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors. Test the implementation with the following example: Input: 1 -- 2 -- 3, Output: A deep copy of the graph.

How do you ensure high code quality in your projects, and what specific practices do you implement to maintain it?