#489 Asynchronous Order Processing Pipeline

Implement an asynchronous pipeline for processing digital-book orders:

• The system must accept orders;
• Validate them;
• Enrich them with data;
• Apply business rules.

Main acceptance criteria:

• The application compiles and starts;
• The application contains a complete order-processing pipeline;
• The number of orders per hour and per minute can be configured;
• All scenarios are handled: success, errors, and limits;
• Messages pass through the entire pipeline end to end;
• Required-field validation is implemented;
• Error handling is implemented.

Optional advanced requirements:

• Stateful processing for limit checks;
• A Circuit Breaker for HTTP calls;
• A retry mechanism with exponential backoff;
• Metrics and monitoring;
• Unit tests for the key logic.