Ktor 3.4.0: native OpenAPI, duplex streaming, Zstd compression & more

Ktor 3.4.0 introduces native OpenAPI generation via a new API and compiler plugin, enabling dynamic, code-driven documentation. The OkHttp client now supports duplex streaming for HTTP/2 connections, allowing bidirectional data transfer. Zstd compression support has also been added for improved server performance with configurable settings. Additional features include a plugin for structured concurrency that cancels in-flight HTTP requests if a client disconnects.