Leetcode 1476. Subrectangle Queries

Implement a class that stores an m×n integer matrix and supports assigning a given value to every cell in an axis-aligned subrectangle and retrieving the current value of a single cell. The core challenge is efficiently handling repeated rectangular range-assignments with point queries (range-update / point-query pattern), e.g., by applying updates directly or recording updates and resolving them on demand.