feat: show MCP tool calls in TUI (#836)

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'
```


![image](https://github.com/user-attachments/assets/db4a79bb-4988-46cb-acb2-446d5ba9e058)

codex-rs/Cargo.lock

@@ -597,7 +597,9 @@ dependencies = [
  "codex-core",
  "color-eyre",
  "crossterm",
+ "mcp-types",
  "ratatui",
+ "serde_json",
  "shlex",
  "tokio",
  "tracing",