Adds logic for the `McpToolCallBegin` and `McpToolCallEnd` events in `codex-rs/tui/src/chatwidget.rs` so they get entries in the conversation history in the TUI. Building on top of https://github.com/openai/codex/pull/829, here is the result of running: ``` cargo run --bin codex -- 'what is the weather in san francisco tomorrow' ``` 