code-mode: carry nested tool kind through runtime (#22377)

## Why

Code mode only used nested spec lookup at execution time to rediscover
whether a nested tool should be invoked as a function tool or a freeform
tool.

That information is already present in the enabled tool metadata that
code mode builds to expose `tools.*` and `ALL_TOOLS`, so re-looking it
up from the router was redundant and kept execution coupled to a
separate spec lookup path.

## What Changed

- thread `CodeModeToolKind` through the code-mode runtime `ToolCall`
event and `CodeModeNestedToolCall`
- emit the nested tool kind directly from the V8 callback using the
already-enabled tool metadata
- build nested tool payloads from the propagated kind instead of calling
`find_spec`
- remove the now-unused `find_spec` plumbing from the router and
parallel runtime helpers
- add unit coverage for function vs freeform payload shaping and update
affected router tests

## Testing

- `cargo test -p codex-code-mode`
- `cargo test -p codex-core code_mode::tests`
- `cargo test -p codex-core
extension_tool_bundles_are_model_visible_and_dispatchable`
- `cargo test -p codex-core
model_visible_specs_filter_deferred_dynamic_tools`

codex-rs/tui/src/chatwidget/tests/status_and_layout.rs

@@ -401,6 +401,7 @@ async fn completed_plan_table_tail_skips_provisional_history_insert() {
 }
 
 #[tokio::test]
+#[cfg_attr(target_os = "windows", ignore = "disabled on windows")]
 async fn configured_pet_load_is_deferred_until_after_construction() {
     let (tx_raw, mut rx) = unbounded_channel::<AppEvent>();
     let tx = AppEventSender::new(tx_raw);