Feature/similar products

[AbdullahTaher93]

feat: Implement Similar Products API with hexagonal architecture

• Built Spring Boot reactive API exposing /product/{id}/similar endpoint
• Implemented hexagonal architecture with clean separation of concerns
• Created domain models with validation (Product, ProductId, SimilarProducts)
• Added professional exception handling with structured error responses
• Implemented reactive programming with WebFlux and Mono/Flux
• Created comprehensive unit test coverage for all layers
• Added architecture tests to validate design principles
• Implemented graceful error handling and timeout management
• Added proper logging and monitoring capabilities
• Created DTOs and mappers for API responses
• Configured WebClient for external service integration
• Added domain exceptions with error codes and HTTP status mapping

Architecture: Domain → Application → Infrastructure layers
Testing: Unit tests, reactive testing, architecture validation
Error Handling: Professional exception handling with structured responses
Performance: Reactive programming with timeout and resilience patterns