Act as a Senior Solutions Architect. Design a comprehensive event-driven microservices architecture for a high-frequency trading platform. The system must handle 100k transactions per second with sub-millisecond latency. Define core services (Order Management, Risk Engine, Market Data Gateway), messaging protocols (Kafka vs. RabbitMQ), data consistency strategies (CQRS, Event Sourcing), and fault tolerance mechanisms (Circuit Breakers, Bulkheads). Provide a detailed explanation of the data flow from order entry to execution, including how to handle partial failures and ensure exactly-once semantics.