Add automated test coverage

[georgidhristov]

Description

Add automated test coverage for the middleware and core request/response handling behavior.

Tasks

• Add a dedicated test project
• Add unit tests for core components
• Add integration tests using the sample API
• Cover exception handling and response rendering scenarios

Suggested Areas To Cover

• middleware execution flow
• exception capture
• request body capture
• response body capture
• HTML/debug response rendering
• configuration/options behavior

Expected Result

The project should validate core behavior automatically and reduce regression risk during refactoring.