[rollout_trace] Record core session rollout traces (#18877)

## Summary

Wires rollout trace recording into `codex-core` session and turn
execution. This records the core model request/response, compaction, and
session lifecycle boundaries needed for replay without yet tracing every
nested runtime/tool boundary.

## Stack

This is PR 2/5 in the rollout trace stack.

- [#18876](https://github.com/openai/codex/pull/18876): Add rollout
trace crate
- [#18877](https://github.com/openai/codex/pull/18877): Record core
session rollout traces
- [#18878](https://github.com/openai/codex/pull/18878): Trace tool and
code-mode boundaries
- [#18879](https://github.com/openai/codex/pull/18879): Trace sessions
and multi-agent edges
- [#18880](https://github.com/openai/codex/pull/18880): Add debug trace
reduction command

## Review Notes

This layer is the first live integration point. The important review
question is whether trace recording is isolated from normal session
behavior: trace failures should not become user-visible execution
failures, and recording should preserve the existing turn/session
lifecycle semantics.

The PR depends on the reducer/data model from the first stack entry and
only introduces the core recorder surface that later PRs use for richer
runtime and relationship events.

codex-rs/Cargo.toml

@@ -169,6 +169,7 @@ codex-responses-api-proxy = { path = "responses-api-proxy" }
 codex-response-debug-context = { path = "response-debug-context" }
 codex-rmcp-client = { path = "rmcp-client" }
 codex-rollout = { path = "rollout" }
+codex-rollout-trace = { path = "rollout-trace" }
 codex-sandboxing = { path = "sandboxing" }
 codex-secrets = { path = "secrets" }
 codex-shell-command = { path = "shell-command" }