S25 P0 starter code

[yliang412]

This PR introduces a new primer project that teaches students to implement a straightforward skip list with minimum synchronization requirements while learning C++.

Learning Goals

By the end of this project, students would:

• Have a correct implementation of a skip list that loosely follows the std::map
• Have a deeper understanding of modern C++ fundamentals and STL containers.
• Get exposure to ways to handle concurrency (at the level of a global reader-writer lock).