Add item streaming events (#5546)

Adds AgentMessageContentDelta, ReasoningContentDelta,
ReasoningRawContentDelta item streaming events while maintaining
compatibility for old events.

---------

Co-authored-by: Owen Lin <owen@openai.com>

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -288,6 +288,9 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::EnteredReviewMode(_)
                     | EventMsg::ItemStarted(_)
                     | EventMsg::ItemCompleted(_)
+                    | EventMsg::AgentMessageContentDelta(_)
+                    | EventMsg::ReasoningContentDelta(_)
+                    | EventMsg::ReasoningRawContentDelta(_)
                     | EventMsg::UndoStarted(_)
                     | EventMsg::UndoCompleted(_)
                     | EventMsg::ExitedReviewMode(_)