Extract tool-suggest wire helpers into codex-tools (#16499)

## Why

This is another straight-refactor step in the `codex-tools` migration.

`core/src/tools/handlers/tool_suggest.rs` still owned request/response
payload structs, elicitation metadata shaping, and connector-completion
predicates that do not depend on `codex-core` session/runtime internals.
Per the `AGENTS.md` guidance to keep shrinking `codex-core`, this moves
that pure wire-format logic into `codex-rs/tools` so the core handler
keeps only session orchestration, plugin/config refresh, and MCP cache
updates.

## What changed

- Added `codex-rs/tools/src/tool_suggest.rs` and exported its API from
`codex-rs/tools/src/lib.rs`.
- Moved `ToolSuggestArgs`, `ToolSuggestResult`, `ToolSuggestMeta`,
`build_tool_suggestion_elicitation_request()`,
`all_suggested_connectors_picked_up()`, and
`verified_connector_suggestion_completed()` into `codex-tools`.
- Rewired `core/src/tools/handlers/tool_suggest.rs` to consume those
exports directly.
- Ported the existing pure helper tests from
`core/src/tools/handlers/tool_suggest_tests.rs` to
`tools/src/tool_suggest_tests.rs` without adding new behavior coverage.

## Validation

```shell
cargo test -p codex-tools
cargo test -p codex-core tools::handlers::tool_suggest::tests
just argument-comment-lint
```

codex-rs/tools/src/lib.rs

@@ -19,6 +19,7 @@ mod tool_config;
 mod tool_definition;
 mod tool_discovery;
 mod tool_spec;
+mod tool_suggest;
 mod utility_tool;
 mod view_image;
 
@@ -112,6 +113,13 @@ pub use tool_spec::create_image_generation_tool;
 pub use tool_spec::create_local_shell_tool;
 pub use tool_spec::create_tools_json_for_responses_api;
 pub use tool_spec::create_web_search_tool;
+pub use tool_suggest::TOOL_SUGGEST_APPROVAL_KIND_VALUE;
+pub use tool_suggest::ToolSuggestArgs;
+pub use tool_suggest::ToolSuggestMeta;
+pub use tool_suggest::ToolSuggestResult;
+pub use tool_suggest::all_suggested_connectors_picked_up;
+pub use tool_suggest::build_tool_suggestion_elicitation_request;
+pub use tool_suggest::verified_connector_suggestion_completed;
 pub use utility_tool::create_list_dir_tool;
 pub use utility_tool::create_test_sync_tool;
 pub use view_image::ViewImageToolOptions;