feat: search_tool migrate to bring you own tool of Responses API (#14274)

## Why

to support a new bring your own search tool in Responses
API(https://developers.openai.com/api/docs/guides/tools-tool-search#client-executed-tool-search)
we migrating our bm25 search tool to use official way to execute search
on client and communicate additional tools to the model.

## What
- replace the legacy `search_tool_bm25` flow with client-executed
`tool_search`
- add protocol, SSE, history, and normalization support for
`tool_search_call` and `tool_search_output`
- return namespaced Codex Apps search results and wire namespaced
follow-up tool calls back into MCP dispatch

codex-rs/codex-api/src/requests/responses.rs

@@ -21,6 +21,7 @@ pub(crate) fn attach_item_ids(payload_json: &mut Value, original_items: &[Respon
         | ResponseItem::Message { id: Some(id), .. }
         | ResponseItem::WebSearchCall { id: Some(id), .. }
         | ResponseItem::FunctionCall { id: Some(id), .. }
+        | ResponseItem::ToolSearchCall { id: Some(id), .. }
         | ResponseItem::LocalShellCall { id: Some(id), .. }
         | ResponseItem::CustomToolCall { id: Some(id), .. } = item
         {