refactor(protocol): map canonical tool items to legacy events (#31296)

## Description

This PR adds legacy `EventMsg` mappings for the `TurnItem` types
introduced in [#30282](https://github.com/openai/codex/pull/30282):

- `CommandExecution`
- `DynamicToolCall`
- `CollabAgentToolCall`
- `SubAgentActivity`

When their producers move to canonical `ItemStarted` / `ItemCompleted`,
raw core event consumers can still receive the existing begin/end-style
events. The canonical item lifecycle remains the live source of truth.

We also record the mapped legacy events in rollout trace so the producer
migration preserves the existing tool-runtime trace entries.

## Why

This is the compatibility layer for the follow-up producer migrations.
Splitting it out first keeps each producer PR small and keeps the legacy
mapping in one place.

## What changed

- Added `TurnItem` → legacy `EventMsg` mappings in
`protocol/src/legacy_events.rs`.
- Added the command execution status conversion used by the exec
mapping.
- Added focused coverage for command execution and dynamic tool
mappings.

codex-rs/core/src/session/mod.rs

@@ -1794,6 +1794,9 @@ impl Session {
 
         let show_raw_agent_reasoning = self.show_raw_agent_reasoning();
         for legacy in legacy_source.as_legacy_events(show_raw_agent_reasoning) {
+            self.services
+                .rollout_thread_trace
+                .record_tool_call_event(turn_context.sub_id.clone(), &legacy);
             let legacy_event = Event {
                 id: turn_context.sub_id.clone(),
                 msg: legacy,