[codex] Forward Codex Apps tool call IDs to backend metadata (#19207)

## Summary
- include the outer tool `call_id` in Codex Apps MCP request metadata
under `_meta._codex_apps.call_id`
- preserve existing Codex Apps metadata like `resource_uri` and
`contains_mcp_source`
- add request metadata coverage for both the existing-metadata and
no-existing-metadata cases

## Why
The paired backend change in
[openai/openai#850796](https://github.com/openai/openai/pull/850796)
updates MCP compliance logging to prefer `_meta._codex_apps.call_id`
instead of the JSON-RPC request id. This client change sends that outer
tool call id so the backend can record the model/tool call identifier
when it is available.

This is wire-compatible with older backends because `_meta._codex_apps`
is already reserved backend-only metadata. Backends that do not read
`call_id` will ignore the extra field.

## Testing
- `cargo test -p codex-core request_meta`
- `just fmt`
- `just fix -p codex-core`

codex-rs/core/tests/suite/search_tool.rs

@@ -555,6 +555,7 @@ async fn tool_search_returns_deferred_tools_without_follow_up_tool_injection() -
             .structured_content,
         Some(json!({
             "_codex_apps": {
+                "call_id": "calendar-call-1",
                 "resource_uri": CALENDAR_CREATE_EVENT_RESOURCE_URI,
                 "contains_mcp_source": true,
                 "connector_id": "calendar",
@@ -586,6 +587,7 @@ async fn tool_search_returns_deferred_tools_without_follow_up_tool_injection() -
     assert_eq!(
         apps_tool_call.pointer("/params/_meta/_codex_apps"),
         Some(&json!({
+            "call_id": "calendar-call-1",
             "resource_uri": CALENDAR_CREATE_EVENT_RESOURCE_URI,
             "contains_mcp_source": true,
             "connector_id": "calendar",