Move models.rs to protocol (#2595)

Moving models.rs to protocol so we can use them in `Codex` operations

codex-rs/core/src/lib.rs

@@ -39,7 +39,6 @@ mod conversation_manager;
 pub use conversation_manager::ConversationManager;
 pub use conversation_manager::NewConversation;
 pub mod model_family;
-mod models;
 mod openai_model_info;
 mod openai_tools;
 pub mod plan_tool;