Round Robin Utilities

The `roundrobin` library provides a small collection of round-robin selectors for various distribution needs. It includes `basic()` for plain round-robin, `weighted()` for classic LVS-style weighted round-robin, `smooth()` for Nginx-style smooth weighted round-robin, and `smooth_stateful()` for smooth weighted round-robin with runtime controls like health checks or slow-start. The current version is 0.1.0, released in January 2026, indicating active development.