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/core/tests/suite/client.rs

@@ -515,6 +515,7 @@ async fn resume_replays_image_tool_outputs_with_detail() {
             item: RolloutItem::ResponseItem(ResponseItem::FunctionCall {
                 id: None,
                 name: "view_image".to_string(),
+                namespace: None,
                 arguments: "{\"path\":\"/tmp/example.webp\"}".to_string(),
                 call_id: function_call_id.to_string(),
             }),
@@ -1878,6 +1879,7 @@ async fn azure_responses_request_includes_store_and_reasoning_ids() {
     prompt.input.push(ResponseItem::FunctionCall {
         id: Some("function-id".into()),
         name: "do_thing".into(),
+        namespace: None,
         arguments: "{}".into(),
         call_id: "function-call-id".into(),
     });