Delegate review to codex instance (#5572)

In this PR, I am exploring migrating task kind to an invocation of
Codex. The main reason would be getting rid off multiple
`ConversationHistory` state and streamlining our context/history
management.

This approach depends on opening a channel between the sub-codex and
codex. This channel is responsible for forwarding `interactive`
(`approvals`) and `non-interactive` events. The `task` is responsible
for handling those events.

This opens the door for implementing `codex as a tool`, replacing
`compact` and `review`, and potentially subagents.

One consideration is this code is very similar to `app-server` specially
in the approval part. If in the future we wanted an interactive
`sub-codex` we should consider using `codex-mcp`

codex-rs/core/src/tasks/regular.rs

@@ -28,6 +28,6 @@ impl SessionTask for RegularTask {
         cancellation_token: CancellationToken,
     ) -> Option<String> {
         let sess = session.clone_session();
-        run_task(sess, ctx, input, TaskKind::Regular, cancellation_token).await
+        run_task(sess, ctx, input, cancellation_token).await
     }
 }