Add text element metadata to types (#9235)

Initial type tweaking PR to make the diff of
https://github.com/openai/codex/pull/9116 smaller

This should not change any behavior, just adds some fields to types

codex-rs/core/tests/suite/user_notification.rs

@@ -60,6 +60,7 @@ echo -n "${@: -1}" > $(dirname "${0}")/notify.txt"#,
         .submit(Op::UserInput {
             items: vec![UserInput::Text {
                 text: "hello world".into(),
+                text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
         })