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/json_result.rs

@@ -76,6 +76,7 @@ async fn codex_returns_json_result(model: String) -> anyhow::Result<()> {
         .submit(Op::UserTurn {
             items: vec![UserInput::Text {
                 text: "hello world".into(),
+                text_elements: Vec::new(),
             }],
             final_output_json_schema: Some(serde_json::from_str(SCHEMA)?),
             cwd: cwd.path().to_path_buf(),