chore: save more about turn context in rollout log file (#8458)

### Motivation
- Persist richer per-turn configuration in rollouts so resumed/forked
sessions and tooling can reason about the exact instruction inputs and
output constraints used for a turn.

### Description
- Extend `TurnContextItem` to include optional `base_instructions`,
`user_instructions`, and `developer_instructions`.
- Record the optional `final_output_json_schema` associated with a turn.
- Add an optional `truncation_policy` to `TurnContextItem` and populate
it when writing turn-context rollout items.
- Introduce a protocol-level `TruncationPolicy` representation and
convert from core truncation policy when recording.

### Testing
- `cargo test -p codex-protocol` (pass)

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

@@ -28,6 +28,11 @@ fn resume_history(
         model: previous_model.to_string(),
         effort: config.model_reasoning_effort,
         summary: config.model_reasoning_summary,
+        base_instructions: None,
+        user_instructions: None,
+        developer_instructions: None,
+        final_output_json_schema: None,
+        truncation_policy: None,
     };
 
     InitialHistory::Resumed(ResumedHistory {