Add Casino Engine to Event-Driven Architecture Samples

[nekzabirov]

Summary

Adds nekzabirov/IGaming-Game-Engine to docs/event-driven-architecture.md → Samples.

Why this fits

Casino Engine is a production-grade open-source iGaming/casino engine in Kotlin/Ktor with a non-trivial event-driven layer:

• Sealed `DomainEvent` hierarchy. Concrete events (`SessionOpened`, `SpinPlaced`, `SpinSettled`, `SpinRolledBack`, `RoundFinished`) are all subtypes of a sealed interface
• Compiler-checked routing. `RabbitMqEventPublisher.publish` is one exhaustive `when (event)` that maps each event subtype to its routing key + payload — adding a new event without updating the publisher fails compilation
• Publish-after-commit. Use cases publish events outside the `dbTransaction { }` block; a failed transaction never emits phantom messages
• Immutable aggregates carry events. `Round.finish()` returns `WithEvents(value, events)` so the use case can drain events post-persist; mutable aggregates extend `AggregateRoot` and call `raise(event)`
• One mapper per event type. Each event has a dedicated file in `infrastructure/rabbitmq/mapper/` owning its payload + routing key constant

Production-tested on moonbet.casino and 2k.ua. Apache 2.0.

Checklist

• Separate PR for this category
• Format matches: `user/repo - Description`
• Meaningful description with concrete patterns