Add more bypass methods

[aristath]

No description provided.

[Copilot]

Pull Request Overview

This PR adds multiple bypass methods to disable WordPress XML-RPC functionality, building upon the existing filter-based approach with additional layers of protection.

• Introduces a custom empty XML-RPC server class to replace the default WordPress implementation
• Adds early termination for XML-RPC requests during initialization
• Provides multiple defensive layers against XML-RPC access attempts

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[ilicfilip]

@aristath , it's nitpicking but I think we should either return error in both places (serve_request and init hook) or empty response (not mixed).

I added helper function which returns the error in the XML format (since that is the format used by XMLRPC) and used it in both places, revert the commit if you dont like it.