Add comprehensive Stock Market Simulator architectural plan with OMS microservice design

[Copilot]

This PR addresses the requirement to create a high-level architectural and implementation plan for a stock market simulator supporting FIX/FAST/ITCH protocols with an Order Management System (OMS) as a microservice.

What's Added

A comprehensive architectural plan document (src/nasdaq/doc/plan.md) that provides a complete blueprint for building a production-ready stock market simulator. The plan includes:

Key Components

• Executive Summary: Overview of the system goals and architecture
• Objectives & Goals: Clear business and technical objectives with success metrics
• System Architecture: Microservices design with OMS as the central hub
• Core Components: Detailed specifications for OMS, protocol gateways, market data engine, and risk management
• Technology Stack: Python-based stack with FastAPI, Kafka, PostgreSQL, Redis, and Kubernetes
• Implementation Phases: 4-phase development plan spanning 16 weeks with clear deliverables

Technical Architecture

The plan leverages the existing nasdaq protocol implementations and extends them into a full microservices architecture:

FIX/FAST/ITCH Gateways → OMS → Market Data Engine
                      ↓         ↓
                Risk Engine → Settlement Engine

Development Roadmap

• Phase 1 (Weeks 1-4): Foundation and core OMS
• Phase 2 (Weeks 5-8): Protocol integration enhancement
• Phase 3 (Weeks 9-12): Market data and risk management
• Phase 4 (Weeks 13-16): Advanced features and production readiness

File Structure

The plan defines a comprehensive directory structure that organizes the codebase into logical modules:

• core/ - Business logic and data models
• gateways/ - Protocol handlers (FIX, FAST, ITCH)
• engines/ - Matching, risk, and settlement engines
• infrastructure/ - Database, messaging, and monitoring
• web/ - APIs and user interfaces

Why This Approach

This architectural plan builds upon the existing nasdaq implementations while providing:

1. Scalability: Microservices architecture supporting thousands of concurrent connections
2. Performance: Sub-millisecond order processing targets
3. Maintainability: Clear separation of concerns and modular design
4. Extensibility: Easy addition of new protocols and features
5. Production Readiness: Comprehensive monitoring, security, and deployment considerations

The plan serves as a complete roadmap for transforming the existing protocol implementations into a full-featured trading simulation platform suitable for educational and testing purposes.

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