Range Sum Query Solution

Complete the implementation with the recursive helpers for update and query.

Implementation details:

• Initialize tree size to $4n$ to handle all cases
• Handle empty array edge case
• Recursive helpers pass node index and current range

Testing checklist:

• Single element array
• Query entire array
• Update and re-query
• Multiple updates between queries

Time: $O(n)$ build, $O(\log n)$ update and query. Space: $O(n)$ for the tree.