Refactor CurlX cookie handling and response access

Refactored cookie handling in CurlX to improve file management, error handling, and CookieJar integration. Updated the Response class to expose the body and reason as public readonly properties instead of getter methods. Adjusted method signatures for better type safety and consistency. Updated examples and documentation to use the new public property access for response bodies and to demonstrate CookieJar usage.

Update README.md

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