Zig's New Async I/O

Zig is introducing a new async I/O system that decouples concurrency primitives from execution models. The key change is an injectable Io interface that allows developers to choose between blocking I/O, thread pools, green threads, or stackless coroutines. This design eliminates function coloring issues while maintaining code reusability across different execution contexts. The system includes features like cancellation support, semantic I/O operations (sendFile, vectorized writes), and guaranteed de-virtualization for single implementation scenarios.