Kino: A high-performance Ractor web server for Ruby 4.0

Kino is a high-performance web server for Ruby 4.0+ that uses Ractors to run parallel Ruby code within a single process, eliminating the memory overhead of forking multiple processes like traditional servers such as Puma. Benchmarks show Kino is 1.5-2× faster on I/O-light endpoints and uses about 4-7× less memory than Puma, while also providing production features like graceful shutdown, error handling, and TLS support. The project includes a diagnostic tool (`kino --check`) to identify code incompatibilities with Ractor mode and maintains a familiar Puma-like configuration interface.