Ensure Host Header is forwarded

[sayyidyofa]

For issue #124

This pull request updates the HTTP header rewriting logic in RequestRewriter to ensure the host header is set correctly, and adds a corresponding test to verify this behavior.

Header rewriting improvements:

• Updated the post_process method in RequestRewriter to explicitly set the host header along with the x-forwarded-host header, ensuring both are present and consistent in outgoing requests.

Testing enhancements:

• Added a test in test_header_rewriter_post_process to check that the host header is set to "taxy.dev" after rewriting, improving test coverage for header handling.