Implement support for using RubyLLM (https://rubyllm.com) with Mongoid, so Mongoid-backed applications can persist RubyLLM chats, messages, and related records as Mongoid documents.
Scope
* Investigate what RubyLLM's persistence integration (acts_as_chat / acts_as_message / acts_as_tool_call) expects from ActiveRecord and what is needed to support it on Mongoid.
* Implement the Mongoid integration.
* Add tests and documentation.