Move models.rs to protocol (#2595)

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

codex-rs/protocol/src/lib.rs

@@ -1,6 +1,7 @@
 pub mod config_types;
 pub mod mcp_protocol;
 pub mod message_history;
+pub mod models;
 pub mod parse_command;
 pub mod plan_tool;
 pub mod protocol;