Add ranked tool discovery to JavaScript code mode (#51209)

## What changed

- Add the default-disabled `code_mode_tool_search` feature to expose `await tools.tool_search({query: "...", limit: 8})` in code mode when the model supports tool search.
- Return BM25-ranked deferred tools as `{tools: [{name, description}]}`, including callable names and TypeScript declarations for use in later code cells.
- Filter results through the current step's nested-tool policy before applying the limit, preserving namespace restrictions, normalized identities, description prefixes, and schema budgets.
- Add ranked-search guidance while retaining `ALL_TOOLS` catalog discovery and description overrides.

## Testing

Add coverage for feature and model-capability gating, namespace restrictions, argument validation, schema budgets, and discovery followed by deferred MCP and dynamic tool calls. Extend the scenario snapshot to cover search, invocation, yielding, and completion through `wait`.

GitOrigin-RevId: 092a29dd5f0773c518f53a001b9cafb917422f13

codex-rs/code-mode-protocol/src/lib.rs

@@ -8,8 +8,10 @@ mod session;
 
 pub use description::CODE_MODE_PRAGMA_PREFIX;
 pub use description::CodeModeToolKind;
+pub use description::DeferredToolDiscovery;
 pub use description::EnabledToolMetadata;
 pub use description::ImageDetailVisibility;
+pub use description::TOOL_SEARCH_GUIDANCE;
 pub use description::ToolDefinition;
 pub use description::ToolNamespaceDescription;
 pub use description::augment_tool_definition;