fix: add ellipsis for truncated status indicator (#12540)

#### What

- Add ellipsis truncation of the status indicator, similar to equivalent
truncation done in the footer.
- Extract truncation helpers into separate file



https://github.com/user-attachments/assets/a2d5f22f-8adc-456e-8059-97359194c25c


#### Tests
Updated relevant snapshot tests

codex-rs/tui/src/lib.rs

@@ -80,6 +80,7 @@ mod get_git_diff;
 mod history_cell;
 pub mod insert_history;
 mod key_hint;
+mod line_truncation;
 pub mod live_wrap;
 mod markdown;
 mod markdown_render;