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/src/codex.rs

@@ -2514,6 +2514,11 @@ async fn try_run_turn(
         model: turn_context.client.get_model(),
         effort: turn_context.client.get_reasoning_effort(),
         summary: turn_context.client.get_reasoning_summary(),
+        base_instructions: turn_context.base_instructions.clone(),
+        user_instructions: turn_context.user_instructions.clone(),
+        developer_instructions: turn_context.developer_instructions.clone(),
+        final_output_json_schema: turn_context.final_output_json_schema.clone(),
+        truncation_policy: Some(turn_context.truncation_policy.into()),
     });
 
     sess.persist_rollout_items(&[rollout_item]).await;