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

Kino is a Rust front-end server that runs Ruby 4.0+ Rack 3 apps in parallel Ractors within a single process, avoiding per-core forks. On an 8-core AWS c7a.2xlarge it achieves 1.5–1.7× higher request rates for I/O-light workloads, 25% more CPU-bound throughput, and about one-eighth the memory of a comparable Puma cluster. It provides graceful draining, crash supervision, back-pressure queues, rustls TLS, and diagnostics for Ractor isolation blockers.