Reuse tool runtime for code mode worker

[pakrym-oai]

Summary

• create the turn-scoped ToolCallRuntime before starting the code mode worker so the worker reuses the same runtime and router
• thread the shared runtime through the code mode service/worker path and use it for nested tool calls
• model aborted tool calls as a concrete ToolOutput so aborted responses still produce valid tool output shapes

Testing

• just fmt
• cargo test -p codex-core (still running locally)