enable tool search over dynamic tools (#18263)

## Summary

- Normalize deferred MCP and dynamic tools into `ToolSearchEntry` values
before constructing `ToolSearchHandler`.
- Move the tool-search entry adapter out of `tools/handlers` and into
`tools/tool_search_entry.rs` so the handlers directory stays focused on
handlers.
- Keep `ToolSearchHandler` operating over one generic entry list for
BM25 search, namespace grouping, and per-bucket default limits.

## Why

Follow-up cleanup for #17849. The dynamic tool-search support made the
handler juggle source-specific MCP and dynamic tool lists, index
arithmetic, output conversion, and namespace emission. This keeps source
adaptation outside the handler so the search loop itself is smaller and
source-agnostic.

## Validation

- `just fmt`
- `cargo test -p codex-core tools::handlers::tool_search::tests`
- `git diff --check`
- `cargo test -p codex-core` currently fails in unrelated
`plugins::manager::tests::list_marketplaces_ignores_installed_roots_missing_from_config`;
rerunning that single test fails the same way at
`core/src/plugins/manager_tests.rs:1692`.

---------

Co-authored-by: pash <pash@openai.com>

codex-rs/tools/src/lib.rs

@@ -109,12 +109,12 @@ pub use tool_discovery::ToolSearchResultSource;
 pub use tool_discovery::ToolSearchSource;
 pub use tool_discovery::ToolSearchSourceInfo;
 pub use tool_discovery::ToolSuggestEntry;
-pub use tool_discovery::collect_tool_search_output_tools;
 pub use tool_discovery::collect_tool_search_source_infos;
 pub use tool_discovery::collect_tool_suggest_entries;
 pub use tool_discovery::create_tool_search_tool;
 pub use tool_discovery::create_tool_suggest_tool;
 pub use tool_discovery::filter_tool_suggest_discoverable_tools_for_client;
+pub use tool_discovery::tool_search_result_source_to_output_tool;
 pub use tool_registry_plan::build_tool_registry_plan;
 pub use tool_registry_plan_types::ToolHandlerKind;
 pub use tool_registry_plan_types::ToolHandlerSpec;